Apparatus and method for measuring physiological parameters of mammal subject and applications of same

ABSTRACT

An apparatus for measuring physiological parameters of a mammal subject includes a first sensor system and a second sensor system that are time-synchronized to each other and spatially separated. Each sensor system has a plurality of electronic components and a plurality of flexible and stretchable interconnects that are electrically connecting to different electronic components, and an elastomeric encapsulation layer at least partially surrounding the plurality of electronic components and the plurality of flexible and stretchable interconnects to form a tissue-facing surface and an environment-facing surface. The plurality of electronic components includes a sensor member for measuring at least one physiological parameter of the mammal subject, a system on a chip (SoC) having a microprocessor coupled to the sensor member for receiving data from the sensor member and processing the received data, and a transceiver coupled to the SoC for wireless data transmission and wireless power harvesting.

CROSS-REFERENCE TO RELATED PATENT APPLICATIONS

This PCT application claims priority to and the benefit of U.S. Provisional Patent Application Serial Nos. 62/753,303, 62/753,453 and 62/753,625, each of which was filed Oct. 31, 2018, and is incorporated herein by reference in its entirety, respectively.

This PCT application is related to a co-pending PCT patent application, entitled “SENSOR NETWORK FOR MEASURING PHYSIOLOGICAL PARAMETERS OF MAMMAL SUBJECT AND APPLICATIONS OF SAME”, by John A. Rogers et al., with Attorney Docket No. 0116936.214W02, and a co-pending US patent application entitled “APPARATUS AND METHOD FOR NON-INVASIVELY MEASURING BLOOD PRESSURE OF MAMMAL SUBJECT”, by John A. Rogers et al., with Attorney Docket No. 0116936.215US2, each of which is filed on the same day that this PCT application is filed, and with the same assignee as that of this application, and is incorporated herein by reference in its entirety, respectively.

Some references, which may include patents, patent applications and various publications, are cited and discussed in the description of this invention. The citation and/or discussion of such references is provided merely to clarify the description of the present invention and is not an admission that any such reference is “prior art” to the invention described herein. All references cited and discussed in this specification are incorporated herein by reference in their entireties and to the same extent as if each reference was individually incorporated by reference.

FIELD OF THE INVENTION

The invention relates generally to healthcare, and more particularly, to apparatus and method for measuring physiological parameters of a mammal subject and applications of the same.

BACKGROUND OF THE INVENTION

The background description provided herein is for the purpose of generally presenting the context of the invention. The subject matter discussed in the background of the invention section should not be assumed to be prior art merely as a result of its mention in the background of the invention section. Similarly, a problem mentioned in the background of the invention section or associated with the subject matter of the background of the invention section should not be assumed to have been previously recognized in the prior art. The subject matter in the background of the invention section merely represents different approaches, which in and of themselves may also be inventions. Work of the presently named inventors, to the extent it is described in the background of the invention section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the invention.

Every year, 300,000 neonates are admitted to the neonatal care unit (NICU) in the U.S. The Global Fetal and Neonatal Care Equipment market is expected to grow from $7.32 billion in 2016 to reach $11.86 billion by 2022. Vital sign monitoring systems, however, have largely remained locked in time since the 1970s. Large base units with extensive wires are still attached to numerous electrodes.

Continuous monitoring of vital signs in the NICU is essential to the survival of critically-ill neonates. Conventional medical platforms in the NICU fail, however, to offer a safe, patient-centric mode of operation, largely due to the use of hard-wired, rigid interfaces to the neonate's fragile, under-developed skin. Some groups have developed neonatal vests with embedded sensors and wireless communication capabilities. Others have instrumented neonatal beds. Those systems are impractical because they are bulky and cover a significant surface area of the neonate—which further complicates medical care instead of simplifying it. Up to 90% of NICU babies have scars by age 7, with the number one cause from devices, including sensor leads. Furthermore, the web of wires prevents effective therapeutic skin-to-skin contact and hinders the ability to turn or position the baby. The existing sensor systems also suffer limited capabilities beyond basic vital monitoring parameters and are fundamentally incapable of being realistically adapted for home or remote monitoring.

In addition, none of those systems have been rigorously tested, including in operating NICUs. Other technology is still in the research phase, requiring multiple wires and lacks the intimate skin connection that enables high fidelity sensing, particularly in the context of a neonate that is moving.

Therefore, a heretofore unaddressed need exists in the art to address the aforementioned deficiencies and inadequacies.

SUMMARY OF THE INVENTION

One aspect of the invention is to provide a highly differentiated product with advanced monitoring capabilities, and greater safety features applicable to various market segments, including: low-resource settings where wireless vital sign monitoring systems have not penetrated into neonatal care; and high-resource settings where the invented systems represent the cutting edge, next generation systems for neonatal monitoring. According to the invention, the systems are reliable and safe sensor systems that are fully wireless and compatible with conformal contact with neonatal skin surfaces, and that are compatible with common procedures in the NICU, including under imaging and/or operating conditions, where conventional systems require time and effort with respect to ensuring multiple wires and leads are appropriately connected and in patient contact to ensure appropriate monitoring.

In one aspect, the invention relates to an apparatus for measuring physiological parameters of a mammal subject. The physiological parameters include, but are not limited to, one or more of heart activities including a stroke volume and ejection fraction, oxygenation level, temperature, skin temperature differentials, body movement, body position, breathing parameters, blood pressure, crying time, crying frequency, swallow count, swallow frequency, chest wall displacement, heart sounds, core body position, asynchronous limb motion, speaking, and biomechanical perturbation. The mammal subject can be a living human subject or a living non-human subject. In certain embodiments, physiological parameters of neonates or infants are monitored and measured. It should be appreciated to one skilled in the art that physiological parameters of children or adults can also be monitored and measured in practice the invention.

In one embodiment, the apparatus includes a first sensor system and a second sensor system that are time-synchronized to each other. Each of the first sensor system and the second sensor system has a plurality of electronic components and plurality of flexible and stretchable interconnects that are electrically connecting to different electronic components, and an elastomeric encapsulation layer at least partially surrounding the plurality of electronic components and the plurality of flexible and stretchable interconnects to form a tissue-facing surface and an environment-facing surface. In one embodiment, each of the first sensor system and the second sensor system is attached to a respective position on the mammal subject so that the first sensor system and the second sensor system are spatially separated by a distance. In certain embodiments, the distance between the first sensor system and the second sensor system is adjustable between a minimal distance and a maximal distance.

In one embodiment, the plurality of flexible and stretchable interconnects comprise at least one of serpentine interconnects and zigzag interconnects.

In one embodiment, the plurality of electronic components comprises a sensor member for measuring at least one physiological parameter of the mammal subject, a system on a chip (SoC) having a microprocessor coupled to the sensor member for receiving data from the sensor member and processing the received data, and a transceiver coupled to the SoC for wireless data transmission and wireless power harvesting.

In one embodiment, the SoC comprises at least one of a near-field communication (NFC) interface and a Bluetooth interface. In one embodiment, said transceiver comprises a magnetic loop antenna tuned to compliance with the NFC protocol and configured to allow simultaneous wireless data transmission and wireless power harvesting through a single link.

In another embodiment, the plurality of electronic components of each of the first sensor system and the second sensor systems further comprises a battery for provide power to said sensor system, and the elastomeric encapsulation layer is configured to electrically isolate the battery from the mammal subject during use. In one embodiment, the battery is a rechargeable battery operably recharged with wireless recharging. In one embodiment, the plurality of electronic components of each of the first sensor system and the second sensor system further comprises a failure prevention element that is a short-circuit protection component or a battery circuit to avoid battery malfunction.

In yet another embodiment, the plurality of electronic components of each of the first sensor system and the second sensor system further comprises a power management unit electrically coupled between the SoC and the transceiver.

In one embodiment, each of the first sensor system and the second sensor system further comprises a microfluidic chamber positioned between the tissue-facing surface and the plurality of electronic components configured to mechanically isolate the plurality of electronic components from a skin surface during use. In one embodiment, the microfluidic chamber is at least partially filled with at least one of an ionic liquid and a gel.

In one embodiment, the encapsulation layer comprises channels or conduits configured to facilitate sweat evaporation during use. In another embodiment, the encapsulation layer is optically transparent so as to be compatible with visual inspection of underlying tissue. In certain embodiments, the encapsulation layer is configured to electrically isolate each of the first sensor system and the second sensor system from an electroshock applied to the mammal subject. In one embodiment, the encapsulation layer comprises a flame retardant material.

In one embodiment, each of the first sensor system and the second sensor system is radio translucent and thermally stable so as to be compatible with medical imaging.

In one embodiment, each of the first sensor system and the second sensor system is formed to be stretchable and bendable.

In one embodiment, each of the first sensor system and the second sensor system is formed in a multi-layer structure to mechanically isolate mechanically stiff components in a mechanical island configuration to accommodate bending, twisting or stretching without fracture or substantial degradation of an operating parameter.

In one embodiment, each of the first sensor system and the second sensor system is configured to conformally attach to a skin surface in a conformal contact without an adhesive, wherein a contact force is generated by Van der Waals interaction between the tissue facing surface of each of the first sensor system and the second sensor system and a skin surface during use.

In one embodiment, the adhesive-free conformal contact comprises a wrapped geometry, the sensor member of at least one of the first sensor system and the second sensor system further comprises a fastener connected to an external surface of the encapsulation layer to fasten the sensor member in the wrapped geometry to a mammal subject.

In one embodiment, each of the first sensor system and the second sensor system further comprises an adhesive layer operably attached to the tissue-facing surface of the encapsulation layer, wherein the adhesive layer has a pattern of perforations through open regions.

In one embodiment, the first sensor system is a conformable torso sensor system configured to attach and conform to a torso region of the mammal subject, and the second sensor system is a conformable extremity sensor system configured to attach and conform to a limb or appendage region of the mammal subject.

In one embodiment, the torso sensor system comprises a first electrode and a second electrode as the sensor member; a Bluetooth low energy (BLE) SoC as the SoC; an ECG analog front-end (AFE)/inertial measurement unit (IMU); and a power management integrated circuit (PMIC) and a memory.

In one embodiment, the sensor member of the torso sensor system comprises at least two electrodes spatially separated from each other by an electrode distance, D, for electrocardiogram (ECG) generation. In one embodiment, the at least two electrodes comprise at least one of mesh electrodes and solid electrodes. In one embodiment, the electrode distance D is adjustable between a minimal electrode distance, D_(min), and a maximal electrode distance, D_(max), wherein the minimal electrode distance D_(min) is a distance of said two electrodes when the torso sensor system is in a non-stretched state, and the maximal electrode distance D_(max) is a distance of said two electrodes when the torso sensor system is in a maximally stretched state along the distance.

In another embodiment, the sensor member of the torso sensor system further comprises one or more of an accelerometer for measuring at least one of a position and a movement; an inertial measurement unit (IMU) for measuring at least one of seismocardiography (SCG) and a respiratory rate; and a temperature sensor for measuring temperature.

In one embodiment, the extremity sensor system comprises a Bluetooth low energy (BLE) SoC as the SoC; a PPG analog front-end (AFE); a photodiode/light emitted diode (LED) and an optical detector as the sensor member; and a power management integrated circuit (PMIC) and a memory.

In one embodiment, the extremity sensor system is configured such that a main circuit component including at least the SoC and the transceiver is aligned and operably wrapped around a limb or appendage in a wrap direction; and the sensor member is spatially separated from and electronically connected to the main circuit component, and operably extends in a direction different from the wrap direction to attach to a sensor region that is spatially distinct from the wrapped portion during use.

In one embodiment, the sensor member of the extremity sensor system is conformable to a skin surface and configured as a soft wrap for circumferential attaching to the limb or appendage region.

In one embodiment, the sensor member of the extremity sensor system comprises a photoplethysmogram (PPG) sensor comprising an optical source and an optical detector located within a sensor footprint. In one embodiment, the optical light source comprises light emitting diodes (LEDs).

In another embodiment, the sensor member of the extremity sensor system further comprises one or more of an accelerometer for measuring at least one of a position and a movement; an inertial measurement unit (IMU) for a motion artifact reduction algorithm; and a temperature sensor for measuring temperature.

In one embodiment, at least one of the first sensor system and the second sensor system further comprises a dynamic baseline control module configured to automatically compensate for mammal subject-to-mammal subject variability and generate an effective driving current to ensure sufficient signal-to-noise and avoid saturation. In one embodiment, the driving current is supplied to an LED to generate an optimized light intensity provided to an underlying mammal subject region.

In one embodiment, each of the first sensor system and the second sensor system is encapsulated with a thin film of silicone elastomer so that said sensor system is waterproof.

In one embodiment, each of the first sensor system and the second sensor system has a thickness less than or equal 3 mm.

In one embodiment, each of the first sensor system and the second sensor system has a Young's modulus less than or equal to 1 GPa.

In one embodiment, the apparatus further comprises a reader system that comprises an antenna in communication with said transceiver of each of the first sensor system and the second sensor system for simultaneous wireless data transmission and wireless power delivery. In one embodiment, the reader system further comprises an NFC reader module for receiving wirelessly transmitted data from each of the first sensor system and the second sensor system, and a Bluetooth low energy (BLE) module for transmitting the received data to an external computing device for at least one of real-time display of the monitored physiological parameters, recording of the monitored physiological parameters, and alarm.

In another embodiment, the apparatus further comprises an alarm device for providing at least one of an optical alert and an audio alert when a physiological parameter is out of a pre-defined range. In one embodiment, the alarm device is at least one of an on-board device and an off-board device.

In another aspect, the invention relates to an apparatus for measuring physiological parameters of a mammal subject. In one embodiment, the apparatus includes one or more sensor systems, each of the one or more sensor systems comprises a plurality of electronic components and plurality of flexible and stretchable interconnects that are electrically connecting to different electronic components, wherein the plurality of electronic components comprises a sensor member for measuring at least one physiological parameter of the mammal subject, an SoC having a microprocessor coupled to the sensor member for receiving data from the sensor member and processing the received data, and a transceiver coupled to the SoC for wireless data transmission and wireless power harvesting; and an elastomeric encapsulation layer at least partially surrounding the plurality of electronic components and the plurality of flexible and stretchable interconnects to form a tissue-facing surface and an environment-facing surface, wherein each of the one or more sensor systems is configured to attach and conform to a pre-determined region of the mammal subject, and to be ready time-synchronized with one another.

In one embodiment, the apparatus further includes a reader system that comprises an antenna in communication with said transceiver of each of the first sensor system and the second sensor system for simultaneous wireless data transmission and wireless power delivery. In one embodiment, the reader system further comprises an NFC reader module for receiving wirelessly transmitted data from each of the first sensor system and the second sensor system, and a Bluetooth low energy (BLE) module for transmitting the received data to an external computing device for at least one of real-time display of the monitored physiological parameters, recording of the monitored physiological parameters, and alarm.

In one embodiment, the one or more sensor systems comprises a first sensor system and a second sensor system that are time-synchronized to each other, wherein the first sensor system is a conformable torso sensor system configured to attach and conform to a torso region of the mammal subject, and the second sensor system is a conformable extremity sensor system configured to attach and conform to a limb or appendage region of the mammal subject.

In one embodiment, the sensor member of the torso sensor system comprises at least two electrodes spatially apart from each other for electrocardiogram (ECG) generation.

In one embodiment, the sensor member of the extremity sensor system comprises a photoplethysmogram (PPG) sensor comprising an optical source and an optical detector located within a sensor footprint.

In one embodiment, the sensor member of each of the torso sensor system and the extremity sensor system further comprises one or more of an accelerometer for measuring at least one of a position and a movement; an inertial measurement unit (IMU) for measuring at least one of a movement, a force, an angular rate, and an orientation; and a temperature sensor for measuring temperature.

In one embodiment, the extremity sensor system is configured such that a main circuit component including at least the SoC and the transceiver is aligned and operably wrapped around a limb or appendage in a wrap direction; and the sensor member is spatially separated from and electronically connected to the main circuit component, and operably extends in a direction different from the wrap direction to attach to a sensor region that is spatially distinct from the wrapped portion during use.

In one embodiment, the one or more sensor systems comprises three or more sensor systems time-synchronized to each other, wherein at least one of the three or more sensor systems is a conformable torso sensor system configured to attach and conform to a torso region of the mammal subject. In one embodiment, at least one of the three or more sensor systems is a conformable extremity sensor system configured to attach and conform to a limb or appendage region of the mammal subject.

In yet another aspect, the invention relates to a method for making a sensor system including a plurality of electronic components and a plurality of interconnects electrically connecting to the plurality of electronic components. In one embodiment, the method includes forming an elastomeric layer of an elastomeric material on a substrate; forming a first electrically conductive film on the elastomeric layer; lithographically patterning the interconnects in the first electrically conductive film; assembling the plurality of electronic components onto the patterned interconnects; and encapsulating an entire area of the assembled electronic components onto the patterned interconnects with the elastomeric material, followed by detaching from the substrate, to fabricate the sensor system.

In one embodiment, the elastomeric material comprises PDMS.

In one embodiment, the electrically conductive film is formed of an electrically conductive material including a metal material comprises Au, Ag, or Cu.

In one embodiment, said forming the electrically conductive film comprises laminating a double layered film of the electrically conductive material on the elastomeric layer; and removing a top layer of the double layered film.

In one embodiment, said assembling the plurality of electronic components onto the patterned interconnects comprises connecting a second electrically conductive film for a bridge and a light source to the patterned interconnects.

In one embodiment, the method further includes forming a microfluidic chamber below the plurality of electronic components.

In one embodiment, said forming the microfluidic chamber comprises attaching a layer of the elastomeric material having the microfluidic chamber defined therein to the bottom surface of the elastomeric layer.

In another embodiment, the method further includes injecting a blended solution of at least one of ionic liquid and silica gel into the microfluidic chamber.

In yet another embodiment, the method further includes forming a silicone layer on the bottom of the sensor system.

In a further aspect, the invention relates to a method of non-invasively measuring physiological parameters of a mammal subject. In one embodiment, the method includes conformally contacting a first sensor system at a torso region of the mammal subject and a second sensor system at a limb or appendage region of the mammal subject, respectively, wherein the first sensor system and the second sensor system are spatially separated by a distance, and configured to measuring a torso physiological parameter and an extremity physiological parameter, respectively; and continuously wirelessly transmitting the time synchronized measured torso physiological parameter and extremity physiological parameter to an external reader, thereby non-invasively measuring the physiological parameters of the mammal subject.

In one embodiment, the distance between the first sensor system and the second sensor system is adjustable between a minimum distance and a maximum distance.

In one embodiment, the physiological parameter is obtained from electrical sensing by electrodes; and oxygen sensing by a plethysmograph.

In one embodiment, the method further includes applying a hydrogel between the first sensor system and the second sensor system and underlying tissue of the mammal subject.

In another embodiment, the method further includes measuring at least one additional physiological parameter related to temperature; movement; spatial position; sound; and blood pressure.

In yet another embodiment, the method further includes determining a mammal subject and region-specific optimized driving voltage provided to an optical light source; and powering an LED optical light source with the optimized driving voltage, thereby ensuring the LED optical light source intensity provides sufficient signal to an optical detector without saturating the optical detector.

In one aspect, the invention relates to a non-transitory tangible computer-readable medium storing instructions which, when executed by one or more processors, cause the above-disclosed method.

These and other aspects of the invention will become apparent from the following description of the preferred embodiment taken in conjunction with the following drawings, although variations and modifications therein may be affected without departing from the spirit and scope of the novel concepts of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The following drawings form part of the present specification and are included to further demonstrate certain aspects of the invention. The invention may be better understood by reference to one or more of these drawings in combination with the detailed description of specific embodiments presented herein. The drawings described below are for illustration purposes only. The drawings are not intended to limit the scope of the present teachings in any way.

FIGS. 1A-1I show schematic illustrations and photographic images of an apparatus including ultra-thin, skin-like wireless sensors for full vital signs monitoring in the neonatal intensive care unit (NICU) with comparisons to clinical standard instrumentation, according to embodiments of the invention. FIG. 1A schematically shows a functional block diagram of an apparatus according to certain embodiments of the present invention. FIG. 1B is a schematic illustration of wireless, battery-free modules for recording electrocardiogram (ECG) and photoplethysmogram (PPG) data and skin temperature. The ionic liquid in microfluidic channel contains blue dye for visualization purposes. FIG. 1C shows images of devices draped over the fingers of a life-sized, transparent mannequin hand to illustrate the sizes and physical form factors of these devices. FIG. 1D shows an image of an ECG epidermal electronic system (EES) stretched uniaxially in the horizontal direction by about 16%. FIG. 1E shows a device for capturing PPG data during operation in a lighted and a dark room. FIG. 1F shows NICU setting with a life-sized neonate doll configured with conventional measurement hardware and FIG. 1G shows NICU setting with a bi-nodal (chest and foot) deployment of skin-like wireless devices designed to provide the same functionality and measurement fidelity. FIG. 1H is a functional block diagram showing analog front end and electronic components of each EES, components of the near-field communication (NFC) system on a chip (SoC) including microcontroller, general-purpose input/output (GPIO), and radio interface, with a host reader platform that includes an NFC reader module and a Bluetooth low energy (BLE) interface with circular buffer. FIG. 1I shows a functional block diagram of the two sensor systems according to another embodiment of the invention. The power management unit involves dual power operation mode from primary wireless power transfer and the secondary battery for portability. The ECG EES includes optional electrode for fECG measurement and 6 axial inertial measurement unit (IMU) for seismocardiography (SCG) and respiratory rate measurement on top of ECG analog front end. The PPG EES includes the pulse oximetry analog front end and 6 axial IMU for motion artifact reduction algorithm. Each individual unit is controlled by BLE SoC.

FIGS. 2A-2I show fundamental aspects of mechanical stresses and soft adhesion at the interface with the skin, according to one embodiment of the invention. FIG. 2A shows simulation results for the deformed geometry and distribution of strain in the copper layer of an ECG EES during uniaxial stretch (about 16%) and for FIG. 2B, the distribution of shear (upper frames) and normal (lower frames) stresses at the interface between an ECG EES and underlying skin interface during deformation for devices without (left) and with (right) the microfluidic channel. Stresses in the latter case are less than about 20 kPa, the threshold of skin sensation. FIG. 2C shows simulation results for the distribution of von Mises stress on the skin due to peeling of a conventional NICU adhesive (left) and the ECG EES adhesive (right). FIG. 2D shows simulation result for the time dependence of the peel force during removal of a conventional NICU adhesive and the ECG EES adhesive from the skin. FIG. 2E shows images that highlight experimental studies of peeling of a conventional NICU adhesive (left) and the ECG EES adhesive (right) from the skin of a healthy adult. FIG. 2F shows experimental measurement of the time dependence of the peel force during removal of a conventional NICU adhesive and the ECG EES adhesive from the skin. FIG. 2G shows simulation results that highlight the role of the microfluidic channel in the peel force associated with removal of an ECG EES from the skin, with emphasis on the initial, non-steady state regime during peel initiation. The circles denote the instants of initial delamination, when the interfacial cohesive strength is reached. The inset shows the normal stress distribution, σyy, along the interface at the instant of initial delamination, where its peak is the cohesive strength. FIG. 2H shows the computed peel force as a function of time for an EES adhesive with the triangular pattern of small holes (diameter D=200 μm) on the skin. The hole area fraction is α=√3πD²/(6L²). FIG. 2I shows the computed peel force as a function of time for triangular and square patterns of large holes (diameter D=1 mm) with the hole area fraction α=35%, where α=πD²/(4L²) and α=√3πD²/(6L²) for square and triangular patterns, respectively.

FIGS. 3A-3N show theoretical and experimental aspects of radiolucency, according to one embodiment of the invention. FIG. 3A shows computational results for the distributions of the in-plane gradient of the magnetic field density associated a mesh electrode (FIG. 1B, top panel), a solid electrode (no mesh; middle) and a commercial NICU electrode (right) for conditions associated with an MRI scan at 128 MHz. FIG. 3B shows Calculated in-plane gradients of the magnetic field density associated with a complete ECG EES at 128 MHz. FIG. 3C shows distributions of the in-plane gradient of the magnetic field density associated a mesh electrode (FIG. 1B, bottom panel), a solid electrode (no mesh; middle) and a commercial NICU electrode (right) for conditions associated with an MRI scan at 128 MHz. FIG. 3D shows the out-of-plane gradients of magnetic field density induced on the ECG EES at 128 MHz. FIG. 3E shows the in-plane gradient of the magnetic field density evaluated along the horizontal dashed lines in panel FIG. 3A. FIG. 3F shows the out-of-plane gradient of the magnetic field density along the horizontal dashed lines in panel FIG. 3C. FIG. 3G shows S11 parameter of the ECG EEG as a function of frequency. The vertical dashed lines indicate operating frequencies of 1.5 T, 3 T, 7 T and 9.4 T MRI scanners at 64 MHz, 128 MHz, 298 MHz and 400 MHz, respectively. FIG. 3H shows computational results for the maximum change in temperature of an ECG EES on skin during an MRI scan.

FIG. 31 shows temperature changes collected using two fiber-optic thermometers located at the interface between an ECG EES (at the loop antenna) and a piece of phantom skin (blue) and on the surface of the phantom skin (red) during MRI scanning (3 T MRI). FIG. 3J shows temperature changes collected by two fiber-optic thermometers at the interface between an ECG EES (at one of the mesh electrodes) and a piece of phantom skin (blue) and on the surface of the phantom skin (red) during MRI scanning (3 T MRI). FIG. 3K shows a coronal MRI image collected from the mid-dorsum of a rat cadaver with an ECG EES mounted on the skin. FIG. 3L shows a coronal MRI image collected from the mid-dorsum rat cadaver with conventional ECG leads mounted on the skin. FIG. 3M shows an X-ray image collected from the right flank of a rat cadaver with an ECG EES mounted on the skin. FIG. 3N shows an X-ray image collected from the right flank of a rat cadaver with conventional ECG leads mounted on the skin.

FIGS. 4A-4J show operational characteristics of the ECG EES, according to one embodiment of the invention. FIG. 4A shows a block diagram of in-sensor analytics for peak detection from ECG waveforms. FIG. 4B shows ECG signals acquired simultaneously from an ECG EES (blue) and a gold standard (red), with detected peaks (green). FIG. 4C shows comparison of heart rate determined using data from the ECG EES and a gold standard. FIG. 4D shows a respiration rate extracted from oscillations of the amplitudes of peaks extracted from the ECG waveforms. FIG. 4E shows comparison of respiration rate determined using data from the ECG EES and manual count by a physician. FIG. 4F shows comparison of skin temperature determined by the ECG EES and a gold standard thermometer. FIG. 4G shows a thermal image of the chest collected using an IR camera. FIG. 4H shows Temperature wirelessly measured using an ECG EES. FIG. 4I shows a Bland Altman plot for heart rate collected from three healthy adults using an ECG EES and a clinical standard system. FIG. 4J shows a Bland Altman plot for respiratory rate collected from three healthy adults using an ECG EES and a clinical standard system.

FIGS. 5A-5L show operational characteristics of the PPG EES, according to one embodiment of the invention. FIG. 5A shows a block diagram of in-sensor analytics for detection of peaks and valleys from PPG waveforms and for dynamic baseline control. FIG. 5B shows A circuit diagram with GPIO enabled baseline control scheme. FIG. 5C shows a demonstration of dynamic baseline level control with a sinusoidal input (blue) and corresponding output changes (red). FIG. 5D shows a demonstration of operation of a PPG EES with (blue and red) and without (black dot) dynamic baseline control. Analytics on baseline level serves as an input to a control system that combines a GPIO port on the NFC SoC with an offset to ensure that the signal input to the ADC lies within its dynamic range (orange). FIG. 5E shows convention for calculating direct and alternating components of PPG waveforms collected in the red and IR, for purposes of calculating SpO₂. FIG. 5F shows empirical formula for SpO₂ calculation using R_(oa) based on comparison to a commercial pulse oximeter. FIG. 5G shows SpO₂ determined using in-sensor analytics during a period of rest followed by a breath hold and then another period of rest. FIG. 5H shows convention for measuring pulse arrival time (PAT) from R-peaks in the ECG waveforms and valley of the PPG waveforms. FIG. 5I shows values of 1/PAT acquired using an ECG EES and a PPG EES and systolic BP data acquired using a cuff monitor. FIG. 5J shows correlation curve between PAT and systolic BP with linear fit. FIG. 5K shows Bland Altman for SpO₂ collected from three adults using a PPG EES and a clinical standard system. FIG. 5L shows a temperature plot showing the capability for measuring differential skin temperatures between the torso and the foot using an ECG EES and PPG EES.

FIGS. 6A-6G show data collection from neonates in clinical and home settings, according to one embodiment of the invention. FIG. 6A shows an image of a healthy term neonate with an ECG EES and a PPG EES on the chest and the bottom of the foot, respectively. FIG. 6B shows an image of a mother holding a healthy term neonate showing skin-to-skin interaction with an ECG EES mounted on the chest. FIG. 6C shows an ECS EES mounted on the back. FIG. 6D shows another image of a mother holding her neonate in the NICU with a magnified view of the ECG EES in the inset. FIG. 6E shows an image of a neonate in the NICU with a PPG EES mounted on an alternative location on the hand. FIG. 6F shows representative ECG and PPG waveforms acquired in this manner from a healthy term neonate. FIG. 6G shows comparison of vital signs calculated from the ECG EES and a gold standard. Temperature and PAT data are displayed without reference data as these measurements are only periodically acquired with conventional hardware.

FIGS. 7A-7G show data collection from neonates in operating neonatal intensive care units, according to one embodiment of the invention. FIG. 7A shows a Bland Altman plot for HR using data from an ECG EES and a clinical standard. FIG. 7B shows a Bland Altman plot for RR using data from an ECG EES and a clinical standard. FIG. 7C shows a Bland Altman plot for SpO₂ using data from a PPG EES and a clinical standard. FIG. 7D shows representative results for PAT determined using combined data from an ECG EES and a PPG EES. FIG. 7E shows differential temperature data collected from an ECG EES and a PPG EES for three recruited neonates with GA of 28 weeks, (FIG. 7F) 29 weeks, and (FIG. 7G) 40 weeks. The other data presented here were collected from this same set of neonates.

FIGS. 8A-8B show PPG EES operating while immersed in soapy water (FIG. 8A) with and (FIG. 8B) without external lighting, according to one embodiment of the invention.

FIGS. 9A-9B show electromagnetic characteristics including inductance, Q factors, and S11 of (FIG. 9A) ECG EES and (FIG. 9B) PPG EES, according to one embodiment of the invention.

FIGS. 10A-10I show a schematic illustration of the process for fabricating the ECG EES and PPG EES, according to one embodiment of the invention. FIG. 10A shows PDMS-coated glass slide substrate (FIG. 10B) laminated with a double layered copper foil, 18/5 μm thick, with the 5 μm thick side facing down. FIG. 10C shows after removal of the 18 μm thick Cu side, photoresist was spin-cast to (FIG. 10D) lithographically pattern the NFC coil and interconnects in the Cu layer. FIG. 10E shows electrical circuit components were assembled onto the Cu circuit. FIG. 10F shows a second metal layer for the bridge and red/IR LEDs were connected to the first metal interconnects with the back side insulated by a thin PDMS coating. FIG. 10G shows the entire area of the ECG EES and PPG EES was encapsulated by PDMS layer, detached from the glass slide and then (FIG. 10H) attached to the bottom PDMS substrate with a spin-coated anti-adhesive layer inside the microfluidic channel. FIG. 10I shows the bottom side was covered with a Silbione layer. A syringe with a micro-needle injected a blended solution of ionic liquid and silica gel into the microfluidic space.

FIG. 11A shows photographic images of ECG EES and PPG EES bent around a plastic tube, according to one embodiment of the invention. FIG. 11B shows finite element analysis results of the strain in the copper layer of the ECG EES and PPG EES on microfluid channel bending to a radius of about 6.4 mm and about 5 mm, respectively.

FIGS. 12A-12C show changes of (FIG. 12A) inductance, (FIG. 12B) Q factor, and (FIG. 12C) S11 of the ECG EES when bent, according to one embodiment of the invention.

FIGS. 13A-13C show changes of (FIG. 13A) inductance, (FIG. 13B) Q factor, and (FIG. 13C) S11 of the PPG EES when bent, according to one embodiment of the invention.

FIGS. 14A-14B show a schematic illustration of (FIG. 14A) the cross-section of the ECG EES and PPG EES and (FIG. 14B) the undeformed and uniaxially-stretched ECG EES and PPG EES with an underlying microfluid channel, according to one embodiment of the invention.

FIG. 15A shows photographic images of an undeformed and a uniaxially-stretched (about 16% defined as in FIGS. 14A-14B) ECG EES on microfluid channel, according to one embodiment of the invention. FIG. 15B shows the strain in the copper layer for an ECG EES without microfluid channel during 8% stretching deformation, and the corresponding shear/normal stresses on the skin (FIG. 15C), according to one embodiment of the invention. FIG. 15D shows the strain in the copper layer for an ECG EES with microfluid channel during 16% stretching deformation, and the corresponding shear/normal stresses on the skin (FIG. 15E), according to one embodiment of the invention. For about 16% stretching of ECG EES on a microfluid channel, both the shear and normal stresses on the skin are less than about 20 kPa, the threshold of skin sensation.

FIG. 16A shows photographic images of an undeformed and a uniaxially-stretched (about 13% as shown in FIG. 14B) PPG EES on microfluid channel, according to one embodiment of the invention. FIG. 16B shows the strain in the copper layer for an PPG EES without microfluid channel during 7% stretching deformation, and the corresponding shear/normal stresses on the skin (FIG. 16C), according to one embodiment of the invention. FIG. 16D shows the strain in the copper layer for an PPG EES with microfluid channel during 13% stretching deformation, and the corresponding shear/normal stresses on the skin (FIG. 16E), according to one embodiment of the invention. For about 13% stretching of PPG EES on a microfluid channel, both the shear and normal stresses on the skin are less than about 20 kPa, the threshold of skin sensation.

FIGS. 17A-17C show changes of (FIG. 17A) inductance, (FIG. 17B) Q factor, and (FIG. 17C) S11 of the ECG EES when stretched, according to one embodiment of the invention.

FIGS. 18A-18C show changes of (FIG. 18A) inductance, (FIG. 18B) Q factor, and (FIG. 18C) S11 of the PPG EES when stretched, according to one embodiment of the invention.

FIG. 19 shows a circuit diagram for the ECG EES, according to one embodiment of the invention, showing an RFI filter, an instrumentation amplifier, a band pass filter, and amplifier. The reference voltage (Vref) is the half of supply voltage (VDD) for voltage offset. The raw ECG signal passes through a radio frequency interference (RFI) filter (f_(c)=200 Hz) to suppress electromagnetic interference from the primary RF source. Subsequent amplification occurs via the instrumentation amplifier with a common mode-rejection ratio of 100 dB and input impedance of 100 GΩ (gain=10 V/V). A passive RC high-pass filter (f_(c), =0.5 Hz) eliminates the DC offset. An inverting amplifier with a low-pass filter further amplifies the signal (gain=50 V/V) and prevents aliasing (f_(c)=100 Hz). Using an external analog-to-digital converter may increase the data throughput.

FIG. 20 shows a circuit diagram for a PPG EES, according to one embodiment of the invention, showing LED drivers, transimpedance amplifier, voltage rectifier with a buck converter, and amplifier including high and low pass filter. Each LED operates in a pulsed mode with 50% duty cycle, out of phase with one another, via current supplied through a single LED driver with an electrical output power of 10 mW. The power supply originates from a separate full-wave rectifier and a buck converter, coupled to a single RF harvesting antenna to bypass limitations associated with the internal rectifier on the NFC. The photodiode captures backscattered light associated with operation of each LED. The output passes through a transimpedance amplifier (transimpedance gain=1 V/μA) followed by a passive high-pass filter (f_(c)=0.5 Hz) to eliminate DC offset and an inverting amplifier (gain=40 V/V) with a low-pass filter configuration (f_(c)=5 Hz) to avoid aliasing. The baseline is controlled by general purpose input/output automatically based on the output signal. Using an external analog-to-digital converter may increase the data throughput.

FIG. 21 shows data communication in ISO15693 standards between transponder and reader with a circular buffer designed to properly index samples, according to one embodiment of the invention.

FIG. 22A shows a measurement setup in a NICU setting with an NFC antenna placed unobstructively underneath the mattress, according to one embodiment of the invention. FIG. 22B shows a picture of the NFC/BLE reader system, which includes an NFC receiver antenna, NFC reader module, and BLE module, according to one embodiment of the invention.

FIG. 23 shows cohesive-zone modeling of the EES adhesive/skin interface, where the cohesive strength σ0 represents the initial delamination, δf represents the complete delamination, and G=σ0 δf/2 is the adhesion energy, according to one embodiment of the invention.

FIG. 24 shows a comparison of peel force from a conventional NICU adhesive and ECG EES adhesive, according to one embodiment of the invention.

FIGS. 25A-25C show a cross-sectional view of the conventional NICU adhesive (FIG. 25A), and the EES adhesive with (FIG. 25B) and without (FIG. 25C) the ionic liquid layer, i.e. the microfluidic channel, according to one embodiment of the invention. Their in-plane sizes are all 4 cm×2 cm.

FIG. 26A shows FEA results, and associated mesh, for the deformation of the skin and the EES adhesive with and without the ionic liquid layer (microfluidic channel) at the instant of initial delamination, according to one embodiment of the invention. The contour plots show the distribution of normal stress (σyy). FIG. 26B shows the corresponding separation of the interface between the skin and EES adhesive, according to one embodiment of the invention.

FIG. 27A shows the EES adhesive without holes, according to one embodiment of the invention. FIGS. 27B-27D show the EES adhesive with holes of diameter D: (FIG. 27B) regular triangular pattern; (FIG. 27C) square pattern; and (FIG. 27D) square pattern with 45° rotation, according to one embodiment of the invention.

FIG. 28A show the EES adhesive with regular triangular holes of small diameter D=200 nm, according to one embodiment of the invention. FIG. 28B shows the peel force versus time for different hole area fractions α, according to one embodiment of the invention. FIG. 28C shows the normalized peel force F/(1−α) versus time, according to one embodiment of the invention.

FIG. 29A shows the EES adhesive with square holes of small diameter D=200 μm, according to one embodiment of the invention. FIG. 29B shows the peel force versus time for different hole area fractions α, according to one embodiment of the invention. FIG. 29C shows the normalized peel force F/(1−α) versus time, according to one embodiment of the invention.

FIG. 30A shows the EES adhesive with 45°-rotated square holes of small diameter D=200 μm, according to one embodiment of the invention. FIG. 30B shows the peel force versus time for different hole area fractions α, according to one embodiment of the invention. FIG. 30C shows the normalized peel force F/(1−α) versus time, according to one embodiment of the invention.

FIG. 31A shows the EES adhesive with holes in a regular triangular pattern, with diameter D, according to one embodiment of the invention. The hole area fraction is α=35%. FIG. 31B shows the peel force versus time for the holes with different diameters D=200 μm, 600 μm, and 1000 μm, according to one embodiment of the invention.

FIG. 32A shows the EES adhesive with holes in a square pattern, with diameter D, according to one embodiment of the invention. The hole area fraction is α=35%. FIG. 32B shows the peel force versus time for the holes with different diameters D=200 μm, 600 μm, and 1000 μm, according to one embodiment of the invention.

FIG. 33A shows the EES adhesive with holes in a square pattern with 45° rotation, with diameter D, according to one embodiment of the invention. The hole area fraction is α=35%. FIG. 33B shows the peel force versus time for the holes with different diameters D=200 μm, 600 μm, and 1000 μm, according to one embodiment of the invention.

FIG. 34 shows effective modulus versus hole area fraction α for holes with different patterns, according to one embodiment of the invention.

FIG. 35 shows a minimum work of adhesion strength of the ECG EES (black) and the PPG EES when stretched up to 20%, according to one embodiment of the invention.

FIG. 36A shows a schematic illustration of the electromagnetic simulation model composed of an electrode on the skin and a Helmholtz coil, according to one embodiment of the invention. FIG. 36B shows electrodes with different structures including mesh (geometry for the ECG EES electrodes), solid (i.e. no mesh) and commercial NICU electrodes, according to one embodiment of the invention.

FIG. 37 shows a schematic illustration of the electromagnetic simulation model composed of the ECG EES on the skin and a Helmholtz coil, according to one embodiment of the invention.

FIG. 38 shows the distributions of the in-plane (top) and out-of-plane (bottom) gradients of the magnetic field density induced by a complete ECG EES at its resonant frequency (150 MHz), according to one embodiment of the invention.

FIG. 39A shows the in-plane gradients of the magnetic field density induced by a complete PPG EES at 128 MHz, according to one embodiment of the invention. FIG. 39B shows the out-of-plane gradients of the magnetic field density induced by a complete PPG EES at 128 MHz, according to one embodiment of the invention.

FIG. 40A shows a schematic illustration of the cross-section of the ECG EES, according to one embodiment of the invention. FIG. 40B shows the distribution of the temperature change on the skin at 0.24 s, which corresponds to the time of the maximum temperature change on the skin for an MRI scan, according to one embodiment of the invention.

FIG. 41A shows the maximum temperature change of the PPG EES and skin versus time for an MRI scan, according to one embodiment of the invention. FIG. 41B shows the distribution of the temperature change on the skin at 0.25 s, which corresponds to the time of the maximum temperature change on the skin for an MRI scan, according to one embodiment of the invention.

FIGS. 42A-42C show ECG signal with three limb leads configuration, according to one embodiment of the invention. (FIG. 42A) Lead I, (FIG. 42B) Lead II, (FIG. 42C) Lead III.

FIGS. 43A-43D show a demonstration of compatibility with autoclave sterilization, according to one embodiment of the invention. FIG. 43A shows ECG signal collected with an ECG EES before autoclave sterilization. FIG. 43B shows ECG signal collected with the same device after autoclave sterilization. FIG. 43C shows PPG signal collected with a PPG EES before autoclave sterilization. FIG. 43D shows PPG signal collected with the same device after autoclave sterilization.

FIGS. 44A-44F show modified Pan-Tompkins algorithm for peak detection from ECG signals, according to one embodiment of the invention. FIG. 44A shows a raw signal. FIG. 44B shows a band-pass filtered signal. FIG. 44C shows differentiation of the signal. FIG. 44D shows squaring the signal. FIG. 44E shows moving average applied to the signal. FIG. 44F shows a detected peak with automatically adjusted threshold level.

FIG. 45 shows experimental setup for calibrating the internal temperature sensor of the ECG EES against a thermometer, according to one embodiment of the invention. The process involves operation under water.

FIG. 46 shows an exemplary plot showing V+ levels based on GPIO combinations for dynamic baseline control with four channels, according to one embodiment of the invention. Four channel GPIOs implement 16 different levels with equal step size.

FIG. 47A shows a block diagram of the NFC interface involving synchronization based on the high-frequency clock of reader module, signal processing module explained previously, and storage module in both local and cloud storage, according to one embodiment of the invention.

FIG. 47B shows a cubic spline interpolation applied to sampled ECG and PPG data, according to one embodiment of the invention.

FIG. 48 shows transparency of the ECG EES demonstrated with a plot of transmittance vs wavelength, according to one embodiment of the invention.

FIGS. 49A-49C show Bland Altman plots for data collected using devices similar to the ECG EES and PPG EES platforms described in the main text, but with on-board power supply, for 18 neonates admitted to the NICU, according to one embodiment of the invention. The mean absolute differences for (FIG. 49A) heart rate, (FIG. 49B) blood oxygenation, and (FIG. 49C) respiratory rate are 0.5 beats/min (SD: 3.3 beats/min), 0.06% (SD: 1.8%), and 2.5 respirations/minute (SD: 4.5 breaths/minute), respectively. No adverse events were noted for any of the subjects.

FIGS. 50A-50H show operational characteristics of the ECG EES, according to one embodiment of the invention. FIG. 50A shows a block diagram of in-sensor analytics for peak detection from ECG waveforms. FIG. 50B shows ECG signals acquired simultaneously from an ECG EES (blue) and a gold standard (red), with detected peaks (green). FIG. 50C shows comparison of heart rate determined using data from the ECG EES and a gold standard. FIG. 50D shows respiration rate extracted from oscillations of the amplitudes of peaks are derived from the ECG waveforms. FIG. 50E shows comparison of respiration rate determined using data from the ECG EES and manual count by a physician. FIG. 50F shows comparison of skin temperature determined by the ECG EES and a gold standard thermometer. FIG. 50G shows a thermal image of the chest collected using an IR camera. FIG. 50H shows temperature wirelessly measured using an ECG EES.

FIGS. 51A-51J show Operational characteristics of the PPG EES, according to one embodiment of the invention. FIG. 51A shows a block diagram of in-sensor analytics for detection of peaks and valleys from PPG waveforms and for dynamic baseline control. FIG. 51B shows a circuit diagram with GPIO enabled baseline control scheme. FIG. 51C is a demonstration of dynamic baseline level control with a sinusoidal input (blue) and corresponding output changes (red). FIG. 51D is a demonstration of operation of a PPG EES with (blue and red) and without (black dot) dynamic baseline control. Analytics on baseline level serves as an input to a control system that combines a GPIO port on the NFC SoC with an offset to ensure that the signal input to the ADC lies within its dynamic range (orange). FIG. 51E shows convention for calculating direct and alternating components of PPG waveforms collected in the red and IR, for purposes of calculating SpO2. FIG. 51F shows empirical formula for SpO2 calculation using Roa based on comparison to a commercial pulse oximeter. FIG. 51G shows SpO2 determined using in-sensor analytics during a period of rest followed by a breath hold and then another period of rest. FIG. 51H shows convention for measuring pulse arrival time (PAT) from R-peaks in the ECG waveforms and valley of the PPG waveforms. FIG. 51I shows values of 1/PAT acquired using an ECG EES and a PPG EES and systolic BP data acquired using a cuff monitor. FIG. 51J shows correlation curve between PAT and systolic BP with linear fit.

FIGS. 52A-52E show features of EES with the safety on skin interface and medical imaging and inspection, according to one embodiment of the invention. FIG. 52A shows images of peel force measurement including the setup (left), with a conventional adhesive (middle), and with an ECG EES (right). FIG. 52B shows a measured peel force of a conventional adhesive and an ECG EES. FIG. 52C shows an MRI image of an ECG EES on a chicken thigh in sagittal plane. FIG. 52D shows operation fully immersed in water—which shows operability in high humidity conditions >80% typical of incubators. FIG. 52E summarizes the finite element model validates the experimental results indicating the significant decrease in interface skin stress.

FIG. 53 shows the underlying software enables interoperability with third party platforms, according to one embodiment of the invention. Further capabilities include cloud storage in a HIPAA complaint manner. The receiver may be a tablet, smartphone, or existing vital signs monitor.

FIG. 54 shows an example of one embodiment of a user interface, according to one embodiment of the invention. Wireless wearable sensors that are discoverable are shown on the left panel. Beyond the sensors themselves, our user interface and base displays can also be used to deliver therapeutic benefit. For instance, musical therapy has been shown to be beneficial to neonatal brain development and neonatal stress relief. Existing displays and monitoring systems are only capable of alarms. Also available on the user interface is an avatar that can depict the patient position, such as on the back, side or front.

DETAILED DESCRIPTION OF THE INVENTION

The present invention will now be described more fully hereinafter with reference to the accompanying drawings, in which exemplary embodiments of the present invention are shown. The present invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. Like reference numerals refer to like elements throughout.

The terms used in this specification generally have their ordinary meanings in the art, within the context of the invention, and in the specific context where each term is used. Certain terms that are used to describe the invention are discussed below, or elsewhere in the specification, to provide additional guidance to the practitioner regarding the description of the invention. For convenience, certain terms may be highlighted, for example using italics and/or quotation marks. The use of highlighting and/or capital letters has no influence on the scope and meaning of a term; the scope and meaning of a term are the same, in the same context, whether or not it is highlighted and/or in capital letters. It will be appreciated that the same thing can be said in more than one way. Consequently, alternative language and synonyms may be used for any one or more of the terms discussed herein, nor is any special significance to be placed upon whether or not a term is elaborated or discussed herein. Synonyms for certain terms are provided. A recital of one or more synonyms does not exclude the use of other synonyms. The use of examples anywhere in this specification, including examples of any terms discussed herein, is illustrative only and in no way limits the scope and meaning of the invention or of any exemplified term. Likewise, the invention is not limited to various embodiments given in this specification.

It will be understood that, although the terms first, second, third, etc. may be used herein to describe various elements, components, regions, layers and/or sections, these elements, components, regions, layers and/or sections should not be limited by these terms. These terms are only used to distinguish one element, component, region, layer or section from another element, component, region, layer or section. Thus, a first element, component, region, layer or section discussed below can be termed a second element, component, region, layer or section without departing from the teachings of the present invention.

It will be understood that, as used in the description herein and throughout the claims that follow, the meaning of “a”, “an”, and “the” includes plural reference unless the context clearly dictates otherwise. Also, it will be understood that when an element is referred to as being “on,” “attached” to, “connected” to, “coupled” with, “contacting,” etc., another element, it can be directly on, attached to, connected to, coupled with or contacting the other element or intervening elements may also be present. In contrast, when an element is referred to as being, for example, “directly on,” “directly attached” to, “directly connected” to, “directly coupled” with or “directly contacting” another element, there are no intervening elements present. It will also be appreciated by those of skill in the art that references to a structure or feature that is disposed “adjacent” to another feature may have portions that overlap or underlie the adjacent feature.

It will be further understood that the terms “comprises” and/or “comprising,” or “includes” and/or “including” or “has” and/or “having” when used in this specification specify the presence of stated features, regions, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, regions, integers, steps, operations, elements, components, and/or groups thereof.

Furthermore, relative terms, such as “lower” or “bottom” and “upper” or “top,” may be used herein to describe one element's relationship to another element as illustrated in the figures. It will be understood that relative terms are intended to encompass different orientations of the device in addition to the orientation shown in the figures. For example, if the device in one of the figures is turned over, elements described as being on the “lower” side of other elements would then be oriented on the “upper” sides of the other elements. The exemplary term “lower” can, therefore, encompass both an orientation of lower and upper, depending on the particular orientation of the figure. Similarly, if the device in one of the figures is turned over, elements described as “below” or “beneath” other elements would then be oriented “above” the other elements. The exemplary terms “below” or “beneath” can, therefore, encompass both an orientation of above and below.

Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the present invention belongs. It will be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and the present disclosure, and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein.

As used in this disclosure, “around”, “about”, “approximately” or “substantially” shall generally mean within 20 percent, preferably within 10 percent, and more preferably within 5 percent of a given value or range. Numerical quantities given herein are approximate, meaning that the term “around”, “about”, “approximately” or “substantially” can be inferred if not expressly stated.

As used in this disclosure, the phrase “at least one of A, B, and C” should be construed to mean a logical (A or B or C), using a non-exclusive logical OR. As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items.

As used in this disclosure, the term “spatially separated” refers to two different locations on skin, wherein the two sensor systems disposed on those locations are not in physical contact. For example, one sensor system may be on the torso, and another sensor system on the foot.

As used in this disclosure, the term “mammal subject” refers to a living human subject or a living non-human subject. For the purpose of illustration of the invention, the apparatus and method are applied to monitor and/or measure physiological parameters of neonates or infants. It should be appreciated to one skilled in the art that the apparatus can also be applied to monitor and/or measure physiological parameters of children or adults in practice the invention.

The description below is merely illustrative in nature and is in no way intended to limit the invention, its application, or uses. The broad teachings of the invention can be implemented in a variety of forms. Therefore, while this invention includes particular examples, the true scope of the invention should not be so limited since other modifications will become apparent upon a study of the drawings, the specification, and the following claims. For purposes of clarity, the same reference numbers will be used in the drawings to identify similar elements. It should be understood that one or more steps within a method may be executed in different order (or concurrently) without altering the principles of the invention.

To address the aforementioned deficiencies and inadequacies, the invention in one aspect discloses a pair of ultrathin, battery-free, skin-conformable electronic sensor systems capable of coordinated, wireless collection of vital signs information at clinical-grade levels of precision and accuracy, without any of the limitations of standard, FDA-cleared systems. The foundational advances in engineering science involve strategies for (1) high bandwidth, high fidelity and wireless modes of battery-free operation based on a single, magnetically coupled inductive link, (2) real-time data processing, analytics and adaptive gain modulation performed using computational resources on the sensor platforms themselves, (3) time-synchronized, continuous streaming of data from a complementary pair of devices mounted on different regions of the body and (4) transparent and radiolucent device designs compatible with visual inspection of underlying tissue and by medical imaging techniques based on magnetic resonance, X-rays and others. Successful demonstrations on neonates with gestational ages ranging from 28 weeks to full term, validated in operating NICUs against clinical ‘gold’ standards indicates the devices have a strong positive clinical impact.

The skin-conformable electronic sensor systems according certain embodiments of the invention have advanced capabilities in data transfer, in-sensor analytics and bi-nodal function enable wireless, high fidelity measurement of full vital signs information, including from fragile neonates. The sensors are optionally battery-free, but can be used with batteries and particularly batteries that can be wirelessly charged. The sensor systems also have broad software interoperability, and so are compatible with a range of hardware readers, including handhelds, computers and conventional monitor systems and displays.

The sensors systems are lightweight and in a convenient patch-like form, that are detachably attachable/mountable to skin, for example, with a weight less than 2 g, and dimensions on the order of 6 cm×3.5 cm×0.2 cm, or less, including less than 3 cm×3 cm×0.2 cm.

Physiological parameters that can be measured include, but are not limited to, one or more of heart activities including a stroke volume and ejection fraction, oxygenation level, temperature, skin temperature differentials, body movement, body position, breathing parameters, ballistocardiography, respiratory effort, blood pressure, crying time, crying frequency, swallow count, swallow frequency, chest wall displacement, heart sounds, core body position, asynchronous limb motion, speaking, and biomechanical perturbation.

One aspect of the invention discloses an apparatus for measuring physiological parameters of a mammal subject. FIG. 1A schematically shows a functional block diagram of the apparatus according to certain embodiments of the present invention. In the exemplary embodiments, the apparatus 100 includes a first sensor system 110 and a second sensor system 150 that are time-synchronized to each other, and a microcontroller unit (MCU) (alternatively, a reader system)190 adapted in wireless communication with the first sensor system 110 and the second sensor system 150. In certain embodiments, each of the first sensor system 110 and the second sensor system 150 is in wireless communication with the MCU 190 via a wireless transmission protocol, such as a near field communication (NFC) protocol, or Bluetooth protocol. Specifically, the term “time-synchronized” (or “time-synced”) refers to measurement of a parameter by different sensors, at different locations, that are synchronized in time to allow for measurement of novel physiological parameters. In certain embodiments, each of the first sensor system 110 and the second sensor system 150 is an epidermal electronic system (EES). In certain embodiments, the first sensor system 110 is a conformable torso sensor system configured to attach and conform to a torso region 410 of the mammal subject for recording electrocardiogram (ECG) data and skin temperature; and the second sensor system 150 is a conformable extremity sensor system configured to attach and conform to a limb or appendage region 420 of the mammal subject for recording photoplethysmogram (PPG) data and skin temperature.

FIGS. 1B-1I shows schematic illustrations and photographic images of the apparatus including the torso sensor system 110 and the extremity sensor system 150 for monitoring full vital signs in the neonatal intensive care unit (NICU) with a comparison to clinical standard instrumentation are shown according to embodiments of the invention. As shown in FIGS. 1A and 1G, the torso sensor system 110 (ECG EES 110) and the extremity sensor system 150 (PPG EES 150) are operably attached to a torso region 410 such as the chest and a limb region 420 such as a foot, respectively, of the neonate so that the ECG EES 110 and the PPG EES 150 are spatially separated by a distance L. The distance L between the ECG EES 110 and the PPG EES 150 is adjustable between a minimal distance and a maximal distance.

In one exemplary embodiment shown in FIGS. 1B, 1D and 1H, the torso sensor system 110 is a wireless, battery-free sensor system for recording ECG data and skin temperature and includes a plurality of electronic components 120 and a plurality of flexible and stretchable interconnects 130 electrically connecting to different electronic components, and an elastomeric encapsulation member (including layers 141, 142 and 143 shown in the top panel of FIG. 1B) at least partially surrounding the plurality of electronic components 120 and the plurality of flexible and stretchable interconnects 130 to form a tissue-facing surface 148 and an environment-facing surface 149. The elastomeric encapsulation member is formed of a silicone elastomer, or the like.

The plurality of flexible and stretchable interconnects 130 are serpentine interconnects as shown in FIG. 1B. Other forms of flexible and stretchable interconnects such as zigzag interconnects can also be utilized to practice the invention. The plurality of flexible and stretchable interconnects 130 is formed of any conductive material including a metal material such as Au, Ag, Cu, etc.

The plurality of electronic components 120 includes a sensor member for measuring the physiological parameters such as ECG data. The sensor member includes, but is not limited to, two electrodes 121 and 122 spatially separated from each other by an electrode distance, D, for ECG generation. The electrodes 121 and 122 can be either mesh electrodes (FIGS. 1B and 1D) or solid electrodes. The electrode distance D is adjustable between a minimal electrode distance, D_(min), and a maximal electrode distance, D_(max), where the minimal electrode distance D_(min) is a distance (e.g., D in FIG. 1B) of said two electrodes 121 and 122 when the torso sensor system is in a non-stretched state (FIG. 1B), and the maximal electrode distance D_(max) is a distance (e.g., D2 in FIG. 1CD) of said two electrodes 121 and 122 when the torso sensor system is in a maximally stretched state along the distance direction 101 (FIG. 1D).

As shown in FIG. 1H, the sensor member 123 also includes, but is not limited to, an instrumentation amplifier (e.g., Inst. Amp) electrically coupled to the two electrodes 121 and 122, adapted for eliminating the need for input impedance matching and thus making the amplifier particularly suitable for use in measurement and test equipment, and an anti-aliasing filter (AAF) electrically couple to the instrumentation amplifier and used before a signal sampler to restrict the bandwidth of a signal to approximately or completely satisfy the Nyquist-Shannon sampling theorem over the band of interest.

Referring to FIG. 1H, the plurality of electronic components 120 also includes a system on a chip (SoC) 124 that includes, but is not limited to, a microprocessor unit, e.g., CPU, a near-field communication (NFC) interface, e.g., NFC ISO 15693 interface, general-purpose input/output (GPIO) ports, one or more temperature sensors (Temp. sensor), and analog-to-digital converters (ADCs) in communication with each other, for receiving data from the sensor member 123 and processing the received data.

Still referring to FIG. 1H, the plurality of electronic components 120 includes a transceiver 125 coupled to the SoC 124 for wireless data transmission and wireless power harvesting. In the exemplary embodiment, the transceiver 125 comprises a loop antenna tuned to compliance with the NFC protocol and configured to allow simultaneous wireless data transmission and wireless power harvesting through a single link.

In addition, referring back to FIG. 1B, the torso sensor system 110 also includes a microfluidic chamber (channel) 145 formed between the tissue-facing surface 148 and the plurality of electronic components 120 in the elastomeric encapsulation member and is configured to mechanically isolate the plurality of electronic components 120 from a skin surface of a patient during use. In one embodiment, the microfluidic chamber 145 is at least partially filled with at least one of an ionic liquid and a gel. For example, in the embodiment shown in FIG. 1A, the ionic liquid in microfluidic channel 145 contains blue dye for visualization purposes. Furthermore, two through openings 146 and 147 are defined in the microfluidic channel 145 such that during use the electrodes 121 and 122 are operably in epidermal contact with the skin surface of the patient through the opening 147 and 147, respectively, for measuring the ECG signals.

In one embodiment, the encapsulation layer further comprises channels or conduits configured to facilitate sweat evaporation during use. In another embodiment, the encapsulation layer is optically transparent so as to be compatible with visual inspection of underlying tissue. In certain embodiments, the encapsulation layer is configured to electrically isolate the first sensor system from an electroshock applied to the mammal subject. In one embodiment, the encapsulation layer comprises a flame retardant material.

In one exemplary embodiment shown in FIGS. 1B, 1E and 1H, the extremity sensor system 150 is also a wireless, battery-free sensor system for recording PPG data and skin temperature and includes a plurality of electronic components 160 and a plurality of flexible and stretchable interconnects 170 electrically connecting to different electronic components, and an elastomeric encapsulation member (including layers 181, 182 and 183 shown in the bottom panel of FIG. 1B) at least partially surrounding the plurality of electronic components 160 and the plurality of flexible and stretchable interconnects 170 to form a tissue-facing surface 188 and an environment-facing surface 189. The elastomeric encapsulation member is formed of a silicone elastomer, or the like.

The plurality of flexible and stretchable interconnects 170 are serpentine interconnects as shown in FIG. 1B. Other forms of flexible and stretchable interconnects such as zigzag interconnects can also be utilized to practice the invention. The plurality of flexible and stretchable interconnects 170 is formed of any conductive material including a metal material such as Au, Ag, Cu, etc.

The plurality of electronic components 160 includes a sensor member for measuring the physiological parameters such as PPG data. As shown in FIG. 1H, the sensor member 163 includes a PPG sensor located within a sensor footprint, which has an optical source having an infrared (IR) light emitting diode (LED) 161 and a red LED 162, and an optical detector (PD) electrically coupled to the IR LED 161 and the red LED 162. The sensor member 163 also includes, but is not limited to, an LED driver electrically coupled to the two electrodes 161 and 162 for driving the IR LED 161 and the red LED 162, and a trans Z amplifier electrically coupled to the PD.

Referring to FIG. 1H, the plurality of electronic components 160 also includes a system on a chip (SoC) 164 that includes, but is not limited to, a microprocessor unit, e.g., CPU, a near-field communication (NFC) interface, e.g., NFC ISO 15693 interface, general-purpose input/output (GPIO) ports, one or more temperature sensors (Temp. sensor), and analog-to-digital converters (ADCs) in communication with each other, for receiving data from the sensor member 163 and processing the received data.

Still referring to FIG. 1H, the plurality of electronic components 160 includes a transceiver 165 coupled to the SoC 164 for wireless data transmission and wireless power harvesting. In the exemplary embodiment, the transceiver 165 comprises a loop antenna tuned to compliance with the NFC protocol and configured to allow simultaneous wireless data transmission and wireless power harvesting through a single link.

In addition, referring back to FIG. 1B, the extremity sensor system 150 also includes a microfluidic chamber (channel) 185 formed between the tissue-facing surface 188 and the plurality of electronic components 160 in the elastomeric encapsulation member and is configured to mechanically isolate the plurality of electronic components 160 from a skin surface of the patient during use. In one embodiment, the microfluidic chamber 185 is at least partially filled with at least one of an ionic liquid and a gel. For example, in the embodiment shown in FIG. 1B, the ionic liquid in microfluidic channel 185 contains blue dye for visualization purposes.

In one embodiment, the encapsulation layer further comprises channels or conduits configured to facilitate sweat evaporation during use. In another embodiment, the encapsulation layer is optically transparent so as to be compatible with visual inspection of underlying tissue. In certain embodiments, the encapsulation layer is configured to electrically isolate the second sensor system from an electroshock applied to the mammal subject. In one embodiment, the encapsulation layer comprises a flame retardant material.

In operation, the torso sensor system 110 (ECG EES 110) and the extremity sensor system 150 (PPG EES 150) are in wireless communication with a reader system 190, alternatively, a microcontroller unit (MCU), having an antenna 195. Specifically, the RF loop antennas 125 and 165 in both the torso sensor system 110 (ECG EES 110) and the extremity sensor system 150 (PPG EES 150) are in wireless communication with the antenna 195 and serve dual purposes in power transfer and in data communication, as shown in FIG. 1H. In one embodiment, the reader system 190 also includes, but is not limited to, an NFC ISO 15693 reader, a circular buffer and a Bluetooth Low Energy (BLE) interface, which are configured such that data can be continuously streamed at rates of up to 800 bytes/s with dual channels, which is orders of magnitude higher than those previously achieved in NFC sensors. A key to realizing such high rates is in minimizing the overhead associated with transfer by packaging data into 6 blocks (24 Bytes) in the circular buffer. Here, reading occurs with an NFC host interfaced to a microcontroller in a BLE system configured with this type of customized circular buffer decoding routine shown in FIG. 21. The primary antenna 195 connects to the host system for simultaneous transfer of RF power to the ECG EES 110 and the PPG EES 150. As such, the apparatus can operate at vertical distances of up to 25 cm, through biological tissues, bedding, blankets, padded mattresses, wires, sensors and other materials found in NICU incubators, for full coverage wireless operation in a typical incubator. BLE radio transmission then allows transfer of data to a personal computer, tablet computer or smartphone with a range of up to 20 m. Connections to central monitoring systems in the hospital can then be established in a straightforward manner.

In certain embodiments, the apparatus 100 may have an alarm device (not shown) for providing at least one of an optical alert and an audio alert when a physiological parameter is out of a pre-defined range. In one embodiment, the alarm device is at least one of an on-board device and an off-board device.

In another embodiment as shown in FIG. 1I, the first sensor system 210 and the second sensor system 250 are similar to the first sensor system 110 and the second sensor system 150 shown in FIG. 1H, except that each of the first sensor system 210 and the second sensor system 250 further comprises a battery 205 for provide power to said sensor system, and a power management unit/IC (PMIC) 206 electrically coupled with the battery 205, the SoC 224/264 and the transceiver (antenna) 195. The power management unit 206 operably involves dual power operation mode from primary wireless power transfer and the secondary battery 205 for portability. In addition, the sensor member (or sensor circuit) 223 of the first sensor system (ECG EES) 210 also includes optional electrode for fECG measurement and 6 axial inertial measurement unit (IMU) for seismocardiography (SCG) and respiratory rate measurement on the top of an ECG analog front end (AFE). The sensor member (or sensor circuit) 263 of the second sensor system (PPG EES) 250 also includes also a PPG AFE and 6 axial IMU for motion artifact reduction algorithm. The SoC 224/264 of each of the first sensor system 210 and the second sensor system 250 further comprises a down-sampler and BLE radio. Each of the power management unit 206 and the sensor members 223 and 263 is controlled by BLE SoC 224/264.

In certain embodiments, the battery 205 is a rechargeable battery operably recharged with wireless recharging. In one embodiment, the plurality of electronic components of each of the first sensor system 210 and the second sensor system 250 further comprises a failure prevention element that is a short-circuit protection component or a battery circuit (not shown) to avoid battery malfunction.

In certain embodiments, each of the first sensor system 110/210 and the second sensor system 150/250 is radio translucent and thermally stable so that each of the first sensor system and the second sensor system is compatible with medical imaging including X-ray, CT and/or MRI imaging. According to the invention, with the specific advantage of having a lower radiological shadowing effect, the small thin sensors allow for less perturbation of CT/X-ray imaging. In addition, the sensors generate minimal heat during MRIs allowing for them to remain on body during this imaging modality.

In certain embodiments, each of the first sensor system 110/210 and the second sensor system 150/250 is formed to be stretchable and bendable.

In certain embodiments, each of the first sensor system 110/210 and the second sensor system 150/250 is formed in a multi-layer structure to mechanically isolate mechanically stiff components in a mechanical island configuration to accommodate bending, twisting or stretching without fracture or substantial degradation of an operating parameter.

In certain embodiments, each of the first sensor system 110/210 and the second sensor system 150/250 is configured to conformally attach to a skin surface in a conformal contact without an adhesive, wherein a contact force is generated by Van der Waals interaction between the tissue facing surface of each of the first sensor system and the second sensor system and a skin surface during use.

In certain embodiments, the adhesive-free conformal contact comprises a wrapped geometry, the sensor member of at least one of the first sensor system and the second sensor system further comprises a fastener connected to an external surface of the encapsulation layer to fasten the sensor member in the wrapped geometry to a mammal subject.

In one embodiment, each of the first sensor system and the second sensor system further comprises an adhesive layer operably attached to the tissue-facing surface of the encapsulation layer, wherein the adhesive layer has a pattern of perforations through open regions.

In certain embodiments, at least one of the first sensor system 110/210 and the second sensor system 150/250 comprises a dynamic baseline control module configured to automatically compensate for mammal subject-to-mammal subject variability and generate an effective driving current to ensure sufficient signal-to-noise and avoid saturation. In one embodiment, the driving current is supplied to an LED to generate an optimized light intensity provided to an underlying mammal subject region.

In certain embodiments, each of the first sensor system 110/210 and the second sensor system 150/250 is encapsulated with a thin film of silicone elastomer so that said sensor system is waterproof.

In certain embodiments, each of the first sensor system 110/210 and the second sensor system 150/250 has a thickness less than or equal 3 mm.

In certain embodiments, each of the first sensor system 110/210 and the second sensor system 150/250 has a Young's modulus less than or equal to 1 GPa.

As disclosed above, two sensor systems are utilized to measure the physiological parameters of a mammal subject. In certain aspects, the invention is not limited the two sensor systems. Instead, one sensor system that is discussed above can also be used to measure the physiological parameters. Furthermore, three or more of these sensor systems, each of which is time-synchronized to each other, and spatial separately attached on a respective position of a mammal subject, can also be used to measure the physiological parameters of the mammal subject. In one embodiment, at least one of the three or more sensor systems is a conformable torso sensor system configured to attach and conform to a torso region of the mammal subject, and at least one of the three or more sensor systems is a conformable torso sensor system configured to attach and conform to a torso region of the mammal subject.

Referring now to FIGS. 10A-10I, a process for making a sensor system including a plurality of electronic components 1041 and a plurality of interconnects 1021 and 1022 electrically connecting to the plurality of electronic components 1041 is shown according to one embodiment of the invention. In exemplary embodiment, the process starts with the steps of (a) forming an elastomeric layer 1010 of an elastomeric material, e.g., PDMS, on a substrate 1001 (FIG. 10A); (b) forming a first electrically conductive film 1020 on the elastomeric layer 1010 (FIGS. 10B-10C), (c) lithographically patterning the interconnects 1021 in the first electrically conductive film 1020 (FIGS. 10C-10D); (d) assembling the plurality of electronic components 1041 onto the patterned interconnects 1021 (FIGS. 10E-10F); and (e) encapsulating an entire area of the assembled electronic components 1041 onto the patterned interconnects 1021 with the elastomeric material, e.g. PDMS (FIG. 10G), followed by detaching from the substrate 1001 (FIG. 10G), to fabricate the sensor system.

In one embodiment, the elastomeric material comprises PDMS or other elastomers.

In one embodiment, the electrically conductive film is formed of an electrically conductive material including a metal material comprises Au, Ag, or Cu.

In one embodiment, said forming the electrically conductive film comprises laminating a double layered film 1020 and 1022 of the electrically conductive material on the elastomeric layer 1010 (FIG. 10B); and removing a top layer 1022 of the double layered film (FIG. 10C).

In one embodiment, said assembling the plurality of electronic components 1041 onto the patterned interconnects 1021 comprises connecting a second electrically conductive film 1025 for a bridge and a light source to the patterned interconnects 1021 (FIG. 10F).

In one embodiment, the method further includes forming a microfluidic chamber 1035 below the plurality of electronic components 1041 (FIGS. 10H-10I).

In one embodiment, said forming the microfluidic chamber 1035 comprises attaching a layer 1030 of the elastomeric material having the microfluidic chamber 1035 defined therein to the bottom surface of the elastomeric layer 1010.

In another embodiment, the method further includes injecting a blended solution of at least one of ionic liquid and silica gel into the microfluidic chamber 1035.

In yet another embodiment, the method further includes forming a silicone layer 1002 on the bottom of the sensor system (FIG. 10I).

In addition, the invention also relates to a method of non-invasively measuring physiological parameters of a mammal subject. In one embodiment, the method includes conformally contacting a first sensor system at a torso region of the mammal subject and a second sensor system at a limb or appendage region of the mammal subject, respectively, wherein the first sensor system and the second sensor system are spatially separated by a distance, and configured to measuring a torso physiological parameter and an extremity physiological parameter, respectively; and continuously wirelessly transmitting the time synchronized measured torso physiological parameter and extremity physiological parameter to an external reader, thereby non-invasively measuring the physiological parameters of the mammal subject.

In one embodiment, the distance between the first sensor system and the second sensor system is adjustable between a minimum distance and a maximum distance.

In one embodiment, the physiological parameter is obtained from electrical sensing by electrodes; and oxygen sensing by a plethysmograph.

In one embodiment, the method further includes applying a hydrogel between the first sensor system and the second sensor system and underlying tissue of the mammal subject.

In another embodiment, the method further includes measuring at least one additional physiological parameter related to temperature; movement; spatial position; sound; and blood pressure.

In yet another embodiment, the method further includes determining a mammal subject and region-specific optimized driving voltage provided to an optical light source; and powering an LED optical light source with the optimized driving voltage, thereby ensuring the LED optical light source intensity provides sufficient signal to an optical detector without saturating the optical detector.

In one aspect, the invention relates to a non-transitory tangible computer-readable medium storing instructions which, when executed by one or more processors, cause the above-disclosed method.

It should be noted that all or a part of the methods according to the embodiments of the invention is implemented by hardware or a program instructing relevant hardware.

Yet another aspect of the invention provides a non-transitory computer readable storage medium/memory which stores computer executable instructions or program codes. The computer executable instructions or program codes enable a computer or a similar computing apparatus to complete various operations in the above disclosed method of non-invasively measuring physiological parameters of a mammal subject. The storage medium/memory may include, but is not limited to, high-speed random access medium/memory such as DRAM, SRAM, DDR RAM or other random access solid state memory devices, and non-volatile memory such as one or more magnetic disk storage devices, optical disk storage devices, flash memory devices, or other non-volatile solid state storage devices.

Certain aspects of the invention also relate to an epidermal-mountable device for monitoring physiological parameters of a patient comprising at least two electronically-coupled sensor systems. Each sensor system comprises a plurality of electronic components, including an antenna for wireless transmissions from a sensor to an external reader; an interconnect that electrically interconnects different electronic components; an elastomeric encapsulation layer that surrounds the plurality of electronic components and interconnect to form a bottom tissue-facing surface and a top environment-facing surface; wherein each of the at least two electronically-coupled sensor systems are configured to conform to spatially separate positions on a patient.

In certain embodiments, the interconnect is a flexible and stretchable interconnect that electrically interconnects different strain-sensitive electronic components.

In certain embodiments, the flexible and stretchable interconnects comprise serpentine interconnects.

In certain embodiments, the first sensor system is a conformable torso sensor system configured to epidermally-mount and conform to a torso region; and the second sensor system is a conformable extremity sensor system configured to epidermally mount and conform to a limb or an appendage region.

In certain embodiments, the extremity sensor system comprises a main circuit component configured to wrap around an appendage in a wrapping direction to mount to the appendage during use; and a sensor that is mechanically decoupled and spatially separated from, and electronically connected to, the main circuit component, and that extends in a different direction than the wrapping direction to mount to a sensor region that is spatially distinct from the wrapped portion during use.

In certain embodiments, the sensor is a PPG sensor comprising an optical source and an optical detector located within a sensor footprint that is less than or equal to 5 mm².

In certain embodiments, the PPG sensor mounts to an appendage region such as a foot or a nail with an adhesive and the main circuit component is configured to mount to an appendage such as an ankle without an adhesive.

In certain embodiments, the device further comprises a temperature sensor mechanically decoupled and spatially separated from, and electronically connected to, the main circuit component.

In certain embodiments, at least one of the sensor systems further comprise a microfluidic chamber positioned between the tissue-facing surface and the plurality of electronic components configured to mechanically isolate the plurality of electronic components from a skin surface during use.

In certain embodiments, the conformable torso sensor system electronic components comprise electrodes for electrocardiogram generation.

In certain embodiments, the conformable torso sensor system electronic components further comprise one or more of a three-axis accelerometer for position monitoring; and a temperature sensor for measuring temperature.

In certain embodiments, the conformable extremity sensor system electronic components comprise an optical detector for measuring oxygen level in tissue underlying the conformable limb sensor system by pulse oximetry. In certain embodiments, the extremity sensor is configured to conformally mount to any of a limb region of all four limbs, forehead, chest, back, abdomen for tissue oxygen determination. In certain embodiments, the conformable extremity sensor system electronic components further comprise an optical light source, such as a light emitting diode, and an optical detector.

In certain embodiments, the conformable extremity sensor system electronic components further comprise a three-axis accelerometer for position or movement monitoring; and a temperature sensor for measuring temperature.

In certain embodiments, the sensor systems are configured to measure a physiological parameter selected from one or more of the group consisting of heart activity, including stroke volume, ejection fraction; oxygenation level; temperature; patient movement; patient position; breathing parameter; blood pressure; and a biomechanical perturbation.

In certain embodiments, each of the sensor systems has a footprint area less than or equal to 10 cm².

In certain embodiments, each of the sensor systems have a thickness less than or equal 3 mm.

In certain embodiments, the device wirelessly communicates with an externally-positioned reader and is wirelessly powered.

In certain embodiments, the device is configured to conformally mount to a skin surface without an adhesive, wherein a contact force is generated by Van der Waals interaction between the bottom surface and a skin surface during use.

In certain embodiments, the device has a peel force from the skin selected from a range that is greater than 0 Newton and less than 1 Newton.

In certain embodiments, the device further comprises an adhesive layer connected to the bottom tissue-facing surface of the encapsulation layer, wherein the adhesive layer has a pattern of perforations.

In certain embodiments, the bottom encapsulation layer comprises channels or conduits configured to facilitate sweat evaporation during use.

In certain embodiments, the device is configured to measure a plurality of physiological parameters from a neonate.

In certain embodiments, each of the limb and extremity sensor system have a Young's modulus less than or equal to 1 GPa.

In certain embodiments, the device is capable of undergoing a strain of up to 20% and bending radius as small as 5 mm without fracture.

In certain embodiments, the measurement of the physiological parameter is continuous for an extended time period that is greater than 4 hours.

In certain embodiments, the device further comprises a hydrogel positioned between the bottom-tissue facing surface and a tissue surface during use.

In certain embodiments, the conformal contact is adhesive-free.

In certain embodiments, the adhesive-free conformal contact comprises a wrapped geometry, the sensor member of at least one of the first sensor system and the second sensor system further comprises a fastener connected to an external surface of the encapsulation layer to fasten the sensor member in the wrapped geometry to a patient.

In certain embodiments, the extremity sensor system comprises an optical unit for photoplethysmography on a nail of an individual that is mechanically isolated from a main circuit component comprising a microprocessor and a wireless transmitter.

In certain embodiments, the sensors are conformable to a skin surface and configured as a soft wrap for circumferential mounting to a limb region.

In certain embodiments, the limb region corresponds to a hand or a foot of a neonate.

In certain embodiments, each of the sensors have a footprint less than or equal to 9 cm².

In certain embodiments, the device further comprises a battery to power the sensors, and the elastomeric encapsulation layer is electrically insulative to electrically isolate the battery from a patient during use.

In certain embodiments, the encapsulation layer electrically isolates the sensor from an electroshock applied to a patient, including under an applied cardiac defibrillation stimulus.

In certain embodiments, the device further comprises a failure prevention element that is a short-circuit protection component or a battery circuit to avoid battery malfunction.

In certain embodiments, the elastomeric encapsulation layer comprises a flame retardant material.

In certain embodiments, the device further comprises a multi-layer structure to mechanically isolate mechanically stiff components in a mechanical island configuration to accommodate bending, twisting and/or stretching without fracture or substantial degradation of an operating parameter.

In certain embodiments, the pair of sensor systems wirelessly communicate time-synchronized data to an external reader, including for pulse arrival time and pulse transit time to determine blood pressure.

In certain embodiments, the device has a continuous stream rate that is greater than or equal to 600 bytes/second.

In certain embodiments, the device further comprises further comprises an external reader wirelessly connected to the pair of sensor systems to display and/or record wirelessly transmitted data from each of the sensors of the sensor systems.

In certain embodiments, the device further comprises further comprises a microprocessor operably connected to the sensors for on-board real-time data processing, analytics and adaptive gain modulation.

In certain embodiments, the antenna is a magnetic loop antenna for wireless power generation.

In certain embodiments, the device further comprises a loop antenna.

In certain embodiments, the device further comprises further comprises a rechargeable battery for wireless recharging.

In certain embodiments, the at least two sensor systems together have a peak current consumption of less than 3 mA.

In certain embodiments, the encapsulation layer is optically transparent and sensor systems have open regions for visual inspection of underlying tissue without monitor removal from skin.

In certain embodiments, the device is radio translucent and thermally stable for medical imaging without device removal during medical imaging.

In certain embodiments, spacing between the pair of sensor systems is adjustable.

In certain embodiments, the device further comprises further comprises an alarm for a physiological parameter that is out of a user-defined normal range.

In certain embodiments, the alarm is an optical alert and/or an audio alert on-board or off-board the device.

In certain embodiments, the microfluidic chamber has a volume that is less than or equal to 1 mL.

In certain embodiments, the microfluidic chamber is at least partially filled with a liquid or a gel.

In certain embodiments, the microfluidic chamber is at least partially filled with a blended solution of an ionic fluid and a silica gel.

In certain embodiments, the device further comprises a dynamic baseline control module to automatically compensate for patient-to-patient variability and generate an effective driving current to ensure sufficient signal-to-noise and avoid saturation.

In certain embodiments, the driving current is supplied to an LED to generate an optimized light intensity provided to an underlying patient region.

Certain aspects of the invention further includes method of non-invasively monitoring a physiological parameter of a patient, comprising the steps of providing the above-disclosed device; conformally contacting the sensor systems at spatially separated regions of the patient; continuously wirelessly transmitting a time synchronized measured torso physiological parameter and extremity physiological parameter to an external reader; thereby non-invasively monitoring a physiological parameter of a patient.

In certain embodiments, the conformal contact is without an adhesive and the conformal contact has a duration of at least 8 hours.

In certain embodiments, the method further comprises applying a hydrogel between the device and underlying tissue.

In certain embodiments, the physiological parameter is obtained from electrical sensing by microelectrodes; and oxygen sensing by a plethysmograph.

In certain embodiments, the method further comprises measuring at least one additional physiological parameter that is related to temperature; movement; spatial position; sound; or blood pressure.

In certain embodiments, the method further comprises determining a patient and region-specific optimized driving voltage provided to an optical light source; powering an LED optical light source with the optimized driving voltage; thereby ensuring the LED optical light source intensity provides sufficient signal to an optical detector without saturating the optical detector.

Certain aspects of the invention also disclose a device for measuring a physiological parameter comprising a main circuit component having a microprocessor and a wireless transmitter; a sensor that is mechanically decoupled and spatially separated from, and electronically connected to, the main circuit component; an encapsulation layer that encapsulates the main circuit component and the sensor; wherein during use the device is configured to mount to a patient surface and is completely wireless.

In certain embodiments, the device further comprises a flexible and stretchable interconnect that electronically connects the sensor to the main circuit.

In certain embodiments, the device further comprises a laterally extending wrap region configured to wrappably mount the main circuit component to a patient during use without an adhesive layer between the encapsulation layer and skin; and a sensor extending sensor region configured to mount the sensor in a direction independent of a wrap direction.

In certain embodiments, the sensor is configured to mount to a foot region or a toenail and the main circuit component around an ankle region.

In certain embodiments, the sensor is a PPG sensor.

According to the invention, among other things, relevant differences of the invented sensor systems from conventional sensor systems include: an ultra-low profile form factor with fully wireless functionality. This enables in-hospital and post-discharge monitoring without any wires. Furthermore, the form factor and encapsulation avoid use of harsh adhesives, so that, if necessary, ultra-low adhesives may be used, which is important for ultra-fragile skin and the entire device is compatible with common medical imaging techniques (CT, XR and MRI). Multiple measurements of a vital sign with different sensor platforms increases accuracy and reliability while decreasing risk of false-positives. The platform is versatile, characterized in that many different physiological parameters can be measured, including, but not limited to, the ones listed above. The digital nature of the sensor systems makes them particularly compatible with various software methodologies, including advanced analytics for predictive algorithms.

Provided herein are also methods of monitoring one or more physiological parameters using any of the devices or systems described herein. Also provided are devices for carrying out any of the methods described herein.

These and other aspects of the present invention are further described below. Without intent to limit the scope of the invention, examples according to the embodiments of the present invention are given below. Note that titles or subtitles may be used in the examples for convenience of a reader, which in no way should limit the scope of the invention. Moreover, certain theories are proposed and disclosed herein; however, in no way they, whether they are right or wrong, should limit the scope of the invention so long as the invention is practiced according to the invention without regard for any particular theory or scheme of action.

Example 1 Dual Wireless Epidermal Electronic Systems with In-Sensor Analytics for Neonatal Intensive Care

Existing vital sign monitoring systems in the neonatal intensive care unit (NICU) fail to offer a safe, patient-centric mode of operation, largely due to the necessity of multiple wires connected to rigid electrodes with strongly adherent interfaces to the skin to ensure good contact. Here, we introduce a pair of ultrathin, skin-like electronic sensors whose coordinated operation bypasses limitations of existing technologies. The enabling advances in engineering science include designs that support (1) wireless, battery-free operation, (2) real-time, in-sensor data analytics, (3) time-synchronized, continuous data streaming, (4) soft mechanics and light adhesive interfaces to the skin and (5) compatibility with advanced medical imaging techniques used in the NICU. Studies on neonates admitted to operating NICUs demonstrate performance capabilities that exceed those of the most advanced clinical-standard monitoring systems.

Continuous recording and real-time graphical display of vital signs is essential for critical care. Each year in the U.S., approximately 300,000 neonates, including a large fraction with exceptionally fragile health status due to severe prematurity and very low birth weight (<1500 g), are admitted to neonatal intensive care units (NICUs). Existing monitoring systems for the NICU require multiple electrode/sensor interfaces to the skin, with hard-wired connections to separately located base units that may be stand alone or wall-mounted for heart rate (HR), respiratory rate (RR), temperature, blood oxygenation (SpO₂) and blood pressure (BP). Although such technologies are essential to clinical care, the associated web of wires greatly complicates even the most basic bedside tasks such as turning a neonate from prone to supine. This hardware also interferes with emergency clinical interventions and radiological studies, and impedes therapeutic skin-to-skin contact, colloquially known as kangaroo mother care, between parents and their infant. Most significantly, the adhesives that couple these wired electrodes to the fragile skin of the neonates are a frequent cause of iatrogenic injuries and subsequent scarring.

A fully wireless alternative that eliminates mechanical stresses and potentially reduces injury-risk, and that deploys effectively on the full range of gestational ages encountered in the NICU would represent a significant advance over the existing standard of care. While textile-based sensors are of interest, these technologies retain wired connections across the body and their inability to support an intimate connection to the skin precludes reliable operation at clinical-grade levels of accuracy, particularly with motion. Recent advances in materials science and biomedical engineering serve as the basis for devices that have an ideal, skin-like form factor. Although such systems can support various types of biophysical measurements of physiological health, significant additional advances are needed to meet the challenging requirements of the NICU, where comprehensive, continuous sensing with wireless functionality, clinical-grade measurement fidelity, and mechanical form factors that eliminate risk of harm to exceptionally fragile neonatal skin are essential.

In certain aspects, the invention discloses a wireless, battery-free vital signs monitoring system that exploits a bi-nodal pair of ultrathin, low-modulus measurement modules, each referred to as an epidermal electronic system (EES), capable of softly and non-invasively interfacing onto neonatal skin. Among other things, five essential advances include: (1) techniques for simultaneous wireless power transfer, low noise sensing and high speed data communications via a single link based on magnetic inductive coupling at a radio frequency band that has negligible absorption in biological tissues, (2) efficient algorithms for real-time data analytics, signal processing and dynamic baseline modulation implemented in the highly constrained computing resources available on the sensor platforms themselves, (3) strategies for time-synchronized, continuous streaming of wireless data from two, separately located devices, (4) mechanics designs and strategies in interface adhesion that minimize the risk of iatrogenic skin injury to fragile neonatal skin, and (5) optimized layouts that enable visual inspection of underlying tissue of the skin interface, and radiolucent electrical configurations that allow magnetic resonance imaging (MRI) and X-ray imaging (XR). Successful pilot phase demonstrations on neonates with gestational ages ranging from 28 weeks to full-term in two, tertiary-level NICUs establish quantitative equivalency to clinical standards.

In addition to advanced capabilities in monitoring, the skin-like profile and fully wireless nature of these platforms offer direct therapeutic value by reducing the barriers for skin-to-skin contact between parent and child. The result enables spontaneous interactions with neonates not further encumbered by ventilator support or central vascular lines. Studies indicate that such skin-to-skin contact reduces neonatal mortality, risk of severe infection, and hypothermia while increasing the rate of weight gain and head circumference growth.

Sensor Designs, System Configurations and Wireless, Battery-Free Modes of Operation

FIG. 1B presents schematic representations of an epidermal system comprising two wireless, sensor systems (epidermal electronic systems (EES)) that, when used together in a time-synchronized fashion, constitute an overall bi-nodal platform capable of reconstructing full vital signs information. The time-synchronized aspect of the sensor systems is also generally referred herein as the sensor systems being “electronically coupled”. The epidermal system is, of course, compatible with more than two sensor systems. The electronic layer in each EES incorporates a collection of thin, narrow serpentine metal traces (Cu, 50-100 μm in width, 5 μm in thickness) that interconnect multiple, chip-scale integrated circuit components. One EES mounts on the chest to record electrocardiograms (ECGs; FIG. 1B, top) through skin-interfaced electrodes that comprise filamentary metal mesh microstructures in fractal geometries; the other mounts on an extremity, such as the base of the foot, to record photoplethysmograms (PPGs; FIG. 1B, bottom) by reflection mode measurements. A microfluidic chamber filled with a non-toxic ionic liquid (e.g., 1-ethyl-3-methylimidazolium ethyl sulfate [EMIM][EtSO₄], Sigma-Aldrich) between the electronics and the lower encapsulation layer mechanically strain-isolates the systems from the fragile skin of the neonate. A thin film of silicone elastomer encapsulates the top, the bottom and the sides, to enable operation even when completely immersed in water as shown in FIGS. 8A-8B.

In addition to the electronics, each EES incorporates a magnetic loop antenna (FIGS. 9A-9B) tuned to compliance with near field communication (NFC) protocols and configured to allow simultaneous wireless data transmission and wireless power delivery through a single link. The low conductivity of the ionic liquid allows stable electrical operation in this RF environment. Details of the methods for fabrication are described below and shown in FIGS. 10A-10I. The resulting bi-nodal system captures and continuously transmits ECG, PPG and skin temperature from each EES. From these data, HR, heart rate variability (HRV), RR, SpO₂ and a surrogate of systolic blood pressure (BP) can be extracted, as discussed subsequently.

The images shown in FIG. 1C highlight the overall size and the ultrathin, soft form factor of these systems. Finite element analysis and experimental results indicate that these devices can bend to radii that are much smaller (6.4 mm and 5 mm, respectively; FIGS. 11A-11B) than required (>about 140 mm and >about 50 mm for the chest and foot, respectively, depending on gestational age) to interface with the chest and the limb of each neonate, without adverse mechanical effects on the device or skin. The electromagnetic properties of both the ECG EES and PPG EES undergo negligible changes when stretched and bent in this manner, thus ensuring robust wireless operation mode for data transmission and power harvesting, as shown in FIGS. 12A-12C and 13A-13C, including during with on a moving patient, such as aneonate. Stretching the ECG EES uniaxially by up to 16% (FIG. 1C) and the PPG EES up to 13% results in strains in the electronics and antenna structures that remain below the limits for plastic deformation (about 0.3%; FIGS. 14A-14B, 15A-15E and 16A-16E). Even with 20% stretching the changes in the inductance, Q factor and resonant frequency of the antennas are minimal (<5%), as shown in FIGS. 17A-17C and 18A-18C. FIG. 1E illustrates a PPG EES with its red LED activated, captured with and without external illumination.

Images shown in FIGS. 1F-1G compare clinical standard technologies (FIG. 1F) to the invented devices (FIG. 1G), as deployed on a realistic model of a neonate. Existing systems require a collection of separate electrodes, sensors and limb-strapped systems paired to base units with hard-wired connections. ECG requires three adhesive-backed electrodes with adjoining wires to monitor HR, HRV and RR. Commonly used electrodes for this purpose (e.g., 3M Red Dot™, 3M Company) may require additional adhesives that further increase the risk of skin injury. Measurements of SpO₂ rely on limb-based devices for PPG (e.g., NLCS Neo SpO₂ sensor, Masimo®), typically wrapped around the entire foot, with an additional wired interface. Continuous measurements of skin temperature, necessary to monitor for signs of hypothermia, involve another adhesive-backed sensor (e.g., HNICU-22, DeRoyal®) and adjoining wire. Collectively, then, vital signs monitoring in the conventional manner demands at least four electrodes and one limb-deployed device, with five wires for external connection to yield HR, HRV, RR, skin temperature, and SpO₂.

The block diagram shown in FIG. 1H summarizes the system architecture and overall wireless operation of the systems introduced here. The ECG EES includes two epidermal electrodes, an instrumentation amplifier, analog filters, an inverting amplifier, and an NFC system-on-a-chip (SoC) (FIG. 19). The PPG EES includes a pair of small-scale LEDs that emit in the red (640 nm) and IR (940 nm), a photodiode, LED drivers, an external power circuit, analog filters, an inverting amplifier, and an NFC SoC (FIG. 20). A 14-bit analog-to-digital converter (ADC) operating at a sampling frequency of 200 Hz on the SoCs digitizes the signals captured by each module. The RF loop antennas in both the ECG EES and PPG EES serve dual purposes in power transfer and in data communication.

Since the standard NFC protocol at 13.56 MHz supports only low speed, low fidelity applications in contactless payments, wireless identification and others, significant modification in both the transponder and host reader systems at ISO15693 were required to enable data transfer rates sufficient for NICU monitoring (hundreds of Hz). The results enable continuous streaming of data at rates of up to 800 bytes/s with dual channels, which is orders of magnitude larger than those previously achieved in NFC sensors. A key to realizing such high rates is in minimizing the overhead associated with transfer by packaging data into 6 blocks (24 Bytes) in a circular buffer. Here, reading occurs with an NFC host interfaced to a microcontroller in a Bluetooth Low Energy (BLE) system configured with this type of customized circular buffer decoding routine shown in FIG. 21. The primary antenna connects to the host system for simultaneous transfer of RF power to the ECG EES and the PPG EES. Operation is possible at vertical distances of up to 25 cm, through biological tissues, bedding, blankets, padded mattresses, wires, sensors and other materials found in NICU incubators, for full coverage wireless operation in a typical incubator. BLE radio transmission then allows transfer of data to a personal computer, tablet computer or smartphone with a range of up to 20 m. Connections to central monitoring systems in the hospital can then be established in a straightforward manner.

Low Modulus Mechanics, Soft Interface Adhesion and Implications for Neonatal Skin Safety

The essential mechanics of these systems decrease risks for skin injury relative to existing clinical standards. The global incidence of skin breakdown in hospitalized neonates ranges between 31-45%, with medical devices and associated adhesives being a major iatrogenic cause. Additionally, pressure-related skin injuries occur in 26% of hospitalized infants <3 months of age with 80% directly related to medical devices, where PPG modules are the most common culprit. By age 7, more than 90% of children previously cared for in the NICU exhibit residual scars secondary to monitoring probes, adhesives and invasive medical interventions. Premature neonates are particularly high-risk given that their epidermis and dermis is 40-60% thinner than adult skin with incomplete cornification, greater trans-epidermal water loss and evaporative heat loss, decreased mechanical strength, and greater propensity to scar. The inherently thin, soft physical properties of the sensors reported here allow for significantly reduced skin contact stresses and adhesion via van der Waals forces alone, and without at least strong conventional adhesives. The result lowers the risk of iatrogenic skin injury in premature neonates by reducing the need for additional adhesives. The devices shown in FIG. 1B have effective moduli in the range of 200-300 kPa (FIG. 2A) and induce minimal normal and shear stresses at the skin interface associated with natural motions of the neonate. The mechanical decoupling afforded by the microfluidic channel decreases these stresses by up to a factor of 2.5 (FIG. 2B), relative to otherwise similar designs without the microfluidics.

Experimental and theoretical studies reveal the fundamental aspects of soft adhesion in these systems. Simulations that use the cohesive zone model (FIG. 23) allow quantitative examination of the mechanics associated with removal of conventional adhesives (e.g., Argyle™ Hydrogel Adhesive Baby Tape Strips, Covidien) and EES devices (modeled as an effective medium; FIGS. 2C-2D) from surfaces with mechanical properties reflective of neonatal skin. The differences between the magnitudes of deformations induced in the skin, at identical peel forces, are notable (FIG. 2C). The forces at steady-state peeling rates are different by approximately a factor of about 10 (FIG. 2D), with reductions in the maximum von Mises stress on the skin by a factor of 4.3. Experimental testing on adult skin (FIGS. 2E-2F) shows similar behaviors, including a significant reduction in peel force (about 1000%, FIG. 24) of an EES relative to that of a traditional adhesive. Analysis of these experimental results defines the adhesion energy at the interface between the EES and skin, i.e. G=16 N/m.

The presence of the microfluidic channel, as shown in FIG. 25C, serves a role in determining the adhesion properties of the EES, as shown in FIG. 2G. At steady-state (>2 s), the peel forces (F) with and without the microfluidics are approximately the same, consistent with a scaling relationship that depends only on G and the width of the device, W, as F=G×W. In other words, the adhesion energy defines the steady-state peeling force. At the initiation of peeling, however, in the non-steady state regime when the forces on the skin are most important, the cohesive strength determines the force. Specifically, the interface starts to delaminate when the normal stress reaches about 20 kPa (FIG. 2G, inset). The microfluidic channel reduces the effective modulus of the EES and, as a consequence, increases the ability of the device to deform under applied force. The consequent reduction in the size of the cohesive zone at the delamination front (FIGS. 26A-26B) decreases the peel force for the same peak stress (cohesive strength).

Further reductions can be achieved by the addition of perforations through the open regions of the EES platform, as shown in FIGS. 27B-27D for different patterns of holes. FIG. 2H highlights the peel force, the primary driver of epidermal stripping in fragile neonatal skin, as a function of time during peeling for a regular triangular pattern of holes (diameter D=200 μm). The force scales simply with 1−α (FIGS. 28A-28C), i.e., the area of contact between the EES and the skin. This scaling also applies to other patterns of holes (e.g., FIGS. 29A-29C and 30A-30C for square patterns without and with 45° rotation, respectively). For sufficiently small holes (e.g., 200 μm, or less than 250 μm), the relation between the peel force and time depends only on 1−α and is approximately independent of pattern. Oscillations in the force only appear for holes larger that the characteristic size of the cohesive zone (about 500 μm as in FIG. 2I). An optimized approach to reducing interface stresses and peel forces, therefore, combines microfluidic channel structures with small perforation holes, the latter of which can be naturally accommodated within the open network designs characteristic of epidermal electronics (FIG. 1B).

Compatibility with Medical Imaging Techniques Used in the NICU

These open design layouts, taken together with certain favorable electromagnetic characteristics of the antennas and interconnects, also greatly improve compatibility with medical imaging and clinical inspections relative to existing clinical monitoring hardware. Magnetic resonance imaging (MRI) is one type of imaging modality that is essential in the NICU, due to its ability to deliver precise assessment of white matter, gray matter, and posterior fossa abnormalities with functional capabilities that exceed those of ultrasound. The EES platforms described here exploit designs that minimize disturbances in the time dependent magnetic fields associated with MRI scanning, thereby reducing distortions and shadowing artifacts in the final images and eliminating any parasitic heating from magnetically induced eddy currents. Calculations of the gradients of the magnetic field density near electrodes with different structures (mesh, solid and commercial electrodes, see FIG. 36B) on biological tissues in a 3 T MRI scanner reveal the underlying effects. The results show that mesh electrodes induce the weakest disturbance to the magnetic field among mesh (layout of FIG. 1C), solid (i.e. no mesh) and commercial electrodes with similar overall sizes and geometries (FIGS. 3A and 3C) for both the in plane |∇pB| and out-of-plane gradient |∇zB| of the magnetic field density. The maximum value of |∇pB| for the mesh electrode is roughly a factor of three times smaller than that of the commercial electrode (FIG. 3E); |∇zB| is four times smaller (FIG. 3F). The mesh design, of course, also has significant advantages in its soft, flexible mechanics and associated benefits in interfacial stresses and adhesion.

Additional simulations guide selection of designs that ensure that the resonant frequencies of the EES have no overlap with the working frequencies of typical MRI scanners (64 MHz, 128 MHz, 298 MHz and 400 MHz for 1.5, 3, 7 and 9.4 T MRI scanners, respectively, FIG. 3G), thereby avoiding large gradients of the magnetic field density (FIGS. 3B, 3D and 38). Similar simulations for the PPG EES indicate gradients of the magnetic field density that are smaller than those for the ECG EES (FIGS. 39A-39B). These features allow the devices to remain in place on neonates undergoing MRI imaging, thereby mitigating the risk of injury and complications with removal and re-adhesion.

Experiment and simulation results also yield information on parasitic heating during an MRI scan. Full three-dimensional multi-physics modeling shows that, at the end of single scan for 0.5 ms, the copper layer of an ECG EES undergoes heating by only 1° C. (FIG. 3H). The resultant maximum temperature change at the skin interface is 0.04° C., far below the threshold for sensation, due to the insulating effects of the PDMS and the microfluidic channel. The maximum change in temperature occurs about 0.24 s (FIGS. 3H and 40A-40B) after initiating the scan. This time scale is on the same order as that for heat conduction (0.1 s) in the microfluidic channel (FIGS. 40A-40B).

Experimental measurements support these findings. FIG. 3I shows the change of temperature during an MRI scan (3 T MAGNETOM Prisma, Siemens Healthineers), measured on a sample of phantom skin at a location underneath the ECG EES near the loop antenna and adjacent to the device. The results show a temperature difference of about 0.1° C. FIG. 3J presents measurements in the middle region of the ECG EES where the values of |∇zB| and |∇pB|, are comparable to those of the bare phantom skin. Simulation results for the PPG EES suggest even smaller changes in temperature than those for the ECG EES (FIGS. 41A-41B). Additional testing with another MRI system (9.4 T Bruker Biospec MRI system, Bruker BioSpin Corporation) and an ECG EES placed over cadaveric rat tissue (FIG. 3K) show no observable magnetically induced displacement forces or torques and no measurable changes in temperature. The results meet FDA requirements for an “MRI-safe” label for medical devices. Actual imaging results indicate that the ECG EES causes much less shadowing and image distortion compared to a conventional NICU ECG electrode (FIG. 3L).

Beyond benefits in MRI, the EES eliminates radiopaque wires, thereby improving evaluation by XR imaging, a modality required for 90% of low-birth weight neonates (26). Experimental results show that an ECG EES placed over the same tissue in a rodent model imaged using a CT/XR system (nanoScan PET/CT, Mediso) exhibits improved radiolucency in comparison to standard ECG electrodes and wires (FIGS. 3M-3N). The optical transparency of the silicone and the open mesh designs of the electronics and antenna structures also provide direct visual access to the skin and tissue beneath the sensor (FIG. 48), thereby negating the need to remove the sensor to monitor the underlying skin for signs of infection or irritation.

Real-Time Measurements, In-Sensor Analytics, Data Transmission and Display for Neonatal Critical Care

Exploiting this collection of attractive electronic, mechanical and radiolucent properties for practical use in a NICU environment requires in-sensor processing and data analytics to reduce bandwidth requirements on wireless transmission and to ensure operational robustness. For example, computational facilities on the NFC SoC of the ECG EES can support a streamlined version of the Pan-Tompkins algorithm for accurate, on-board analysis of the QRS complex of ECG signals in real-time to yield HR and HRV on a beat-to-beat basis. FIG. 4A summarizes an approach that starts with digital bandpass filter (f_(c1)=5 Hz, f_(c2)=15 Hz) to attenuate the noise. Differentiating and squaring the resulting data yields the slope of QRS peaks and prevents false peak detection associated with the T wave. Applying a moving average and a dynamic threshold identifies a running estimate of the R peak and the magnitude of the noise. Automatic adjustments of the threshold rely on these estimates for the preceding beat cycle (FIGS. 44A-44F). The R-to-R intervals determined in this way yield the instantaneous HR. Simultaneous recordings obtained using a clinical standard system, henceforth referred to as ‘gold’ standard data, validate the ECG module hardware and in-sensor analytics, via measurements on a healthy adult volunteer (FIGS. 4B-4C). The ECG signals and computed HR values from these two platforms show no measurable differences. Periodic modulations of the amplitude of the R peak define the RR (FIG. 4D), which also agrees with the gold standard (visual counting by a physician in this case; FIG. 4E). Measurements of skin temperature rely on sensors internal to the NFC SoC in each EES, where transmission at a sampling frequency of 1 Hz is sufficient for monitoring purposes. The low thermal mass of the EES and the small thickness of the substrate layer (PDMS; 50 μm in thickness) separates the SoC from the skin to ensure fast thermal response times and excellent thermal coupling, respectively. Comparisons against readings from a thermometer (Fisherbrand™ 13202376, Fisher Scientific) serve as means to calibrate the sensor (FIG. 4F) via testing in a water bath (FIG. 45). Thermal images captured with an IR camera (FLIR A325SC, FLIR Systems) during operation indicate negligible heating associated with the electronics or the antenna structures (FIG. 4G). FIG. 4H shows temperature readings from ECG EES for 60 s. Comparison tests of this system against FDA cleared monitoring equipment (Dash 3000, GE Healthcare) on healthy adult volunteers (n=3) show excellent agreement for HR (mean difference=0.1, standard deviation=2.55, both in bpm) and RR (mean difference=0.3, standard deviation=0.95, both in bpm) as shown in FIGS. 4I-4J, respectively.

The PPG EES relies on similar NFC protocols, but with in-sensor analytic methods that not only reduce requirements on transmission bandwidth but also provide, when used in conjunction with adaptive circuits, crucial functionality for stable operation. Specifically, the processing in this case can enable (i) dynamic baseline control to ensure that the input to the ADC on the NFC SoC lies within the linear response range and (ii) real-time calculation of SpO₂ from the PPG traces (FIG. 5A). Here, the processing begins with application of a moving average filter to the photodetector response from the red and IR LEDs. When the larger of these two averaged PPG amplitudes (typically that associated with the IR response) lies outside of a range that is optimal for the ADC (0.25-0.7 V), a programmable difference amplifier with voltage dividers at V+ dynamically adjust the baseline level. The circuit shown in FIG. 5B demonstrates the operation where the governing equation is

$\begin{matrix} {V_{tr} = {{{- \frac{R_{f}}{R_{s}}}V_{pre}} + {\left( {1 + \frac{R_{f}}{R_{s}}} \right)V_{+}}}} & (1) \end{matrix}$

where V_(tr) is the voltage output of the amplifier, V_(pre) is the voltage of the input signal, R_(s) is the input resistance, R_(f) is the feedback resistance. The voltage divider at V₊ with resistor R_(d1) and R_(d2) governs following equation with Vref of 1.8V

$\begin{matrix} {V_{+} = {\frac{R_{d2}V_{ref}}{R_{d2} + R_{d1}}\left( {\frac{a_{0}}{16} + \frac{a_{1}}{8} + \frac{a_{2}}{4} + \frac{a_{3}}{2}} \right)}} & (2) \end{matrix}$

Sixteen different baseline states can be accessed via activation of binary values from four general purpose input output pins (a₀, a₁, a₂, a₃) on the SoC (FIG. 46), applied through an R-2R resistor ladder. FIG. 5C shows dynamic control of the output voltage (V_(tr)) of a sinusoidal input signal (frequency=50 mHz, amplitude=40 mV, V_(offset)=−30 mV). Starting with the default setting of the GPIO ports (a₀, a₁, a₂, a₃; all high, or 1111), the baseline level automatically adjusts to lower levels associated as the value of V_(tr) drifts above the upper boundary of the specified voltage range, and vice versa as V_(tr) falls below the lower boundary. The result maintains V_(tr) in the allowed range. FIG. 5D summarizes the operation in an actual PPG recording. Without this type of real-time, in-sensor processing (IR Non in FIG. 5D) robust operation would be impossible: PPG signals would quickly drift outside of the narrow operating range of the ADC due to patient-to-patient variations in skin pigmentation and unavoidable, time-dependent fluctuations in optical scattering that result from micro-motions relative to underlying blood vessels and subdermal structures.

Calculating SpO₂ involves determining the ratio (R_(oa)) between the alternating and direct components of the PPG signals according to

$\begin{matrix} {R_{oa} = {\frac{AC_{RED}}{DC_{RED}}/\frac{AC_{IR}}{DC_{IR}}}} & (3) \end{matrix}$

for data from the red and IR LEDs (FIG. 5E). An empirical calibration formula determined by comparison to an FDA-cleared fingertip oximeter measurement (MightySat Fingertip Oximeter, Masimo®) converts the R_(oa) to SpO₂ (FIG. 5F). Time dependent variations of SpO₂ determined in this manner appear in FIG. 5G with demonstration in a decrease with a breath hold in an adult volunteer.

Beyond re-capitulation of well-established vital signs, the time synchronized outputs from the ECG EES and the PPG EES allow for determination of advanced physiological parameters that are of high clinical value but not regularly collected in routine practice in NICUs. A key example is the measurement of pulse arrival time (PAT), defined by the time lapse between the maximum fiducial point in the ECG signal (R peak) and the corresponding minimal fiducial point in the PPG signal at valley as in FIG. 5H, as a direct correlate to systolic blood pressure. Blood pressure is an essential physiological marker of perfusion, autonomic function, and vascular tone for critically ill newborns. Cuff-based blood pressure measurements with sphygmomanometers fail to provide a continuous measurements, overestimate blood pressure in premature neonates, and pose a direct risk for pressure-related injuries. While arterial lines offer a continuous measurement of blood pressure in neonates, these invasive interventions can cause thrombosis, hematomas, infection, and even death. Thus, the ability to capture PAT non-invasively and continuously would be of high clinical value in the NICU with prior reports providing evidence that PAT correlates with blood pressure in infants. The Moens-Korteweg equation provides a linear relationship between PAT and BP. Measurements of 1/PAT performed in processing of ECG and PPG data in the host (FIGS. 47A-47B), together with corresponding values of systolic BP captured using a sphygmomanometer on a healthy adult during a period of rest after exercising (running at 6 miles per hour for 15 minutes), exhibit the expected linear relationship (FIG. 5I). A calibration plot with a linear fit appears in FIG. 5J. The bi-nodal configuration of the system naturally yields not only a surrogate marker of BP but also temperatures at two different locations (trunk and limb), to improve monitoring for hypothermia and provide a noninvasive method to track peripheral perfusion. In current clinical practice, measurements of skin temperature are typically limited to a single body location due to the need to minimize wired connections and adhesive interfaces to the skin. Comparison tests of this system against FDA cleared monitoring equipment (Dash 3000, GE Healthcare) on healthy adult volunteers (n=3) show excellent agreement for SpO₂ (mean difference=0.3, standard deviation=1.37, both in %) as shown in FIG. 5K. FIG. 5L illustrates the ability with an ECG EES and PPG EES to capture differential skin temperature between the torso and peripheral limbs.

Pilot Studies in NICUs and Validation Against Clinical Standards

Preliminary testing of the EES system in both healthy neonates (n=3) and premature infants in two tertiary level NICUs demonstrates feasibility and measurement validity. FIGS. 6A-6C, highlight deployment in a healthy term neonate with an ECG EES and a PPG EES mounted on the chest and the foot, respectively, where van der Waals forces govern the mechanical interface to the skin, with minimal mechanical, mass or thermal load (FIG. 6A; 38 weeks 3/7 gestational age, 2.75 kg birth weight). The silicone encapsulation also enables reliable operation of the systems when completely immersed in water (FIGS. 8A-8B), thereby supporting compatibility with NICU incubators commonly set at humidity above 80% to maintain temperature homeostasis and prevent dehydration in premature neonates.

FIG. 6B illustrates the use in a mode that facilitates physical contact between parent and child, which is difficult or impossible to replicate with hard-wired conventional systems. FIG. 6C shows an alternative mounting location, where the ECG EES resides on the back of the neonate to facilitate chest-to-chest skin interaction, while highlighting the intimate contact with the skin, even while naturally deformed and wrinkled. In FIGS. 6D-6E, the sensor system is on a neonate admitted in the NICU, highlighting intimate contact of the ECG EES to the skin, even with motion and position adjustment. An additional example of skin-to-skin contact in a chest-to-chest position is in FIG. 6E, with the PPG EES on the upper limb to illustrate another option for placement. Representative results of continuous recordings are in FIG. 6F for the neonate presented in FIG. 6A. Calculated HR, SpO₂, and RR compare favorably against gold standard equipment (Intellivue MX800, Philips). The temperature and PAT data appear alone given the absence of a comparator system (FIG. 6G).

Concomitant deployment with standard of care monitors (Intellivue MX800, Philips; Table 1) shows excellent agreement in HR, RR, and SpO₂ (FIGS. 7A-7C) in n=3 neonates ranging in gestational age from 28 to 40 weeks admitted to the NICU. The mean difference is −0.17 beats per minute for HR, 0.76 breathes per minute for respiratory rate, and 1.02% for SpO₂. Advanced physiological parameters such as PAT and continuous differential skin temperature are also shown (FIGS. 7D-7G). Additional studies in n=18 neonates admitted in the NICU with gestational ages as low as 28 weeks and weights as low as 1470 g, using related device platforms with on-board power supply to facilitate testing, further validate the operation and applicability across a large cohort of subjects (FIGS. 49A-49C, Table 1) with excellent agreement with gold-standard monitoring equipment (Intellivue MX800, Philips).

Beyond efficacy and safety, the eventual diffusion of medical technologies depends on economic considerations. Table 2 outlines cost structures associated with all aspects of device construction, ranging from components, to fabrication processing fees and encapsulation materials. The results suggest costs (ECG EES and PPG EES) of less than $20 USDs per unit at scaled production. Full compatibility with autoclave sterilization (2540E, Heidolph) enables safe re-use (FIGS. 43A-43D) and further improved economics, with potential to facilitate deployment in low and middle income countries in the context of global health.

TABLE 1 Clinical characteristics of neonates admitted in the NICU and tested with the battery-free, dual EES system using both battery-free modality (n = 3) and battery-powered version (n = 18). Subject Gestational Age (Weeks) Ethnicity Clinical Validation of Wireless, Battery-Free ECG EES and PPG EES System in the Neonatal Intensive Care Unit 1 28 Hispanic 2 29 Caucasian 3 40 Asian Clinical Validation of Wireless, Battery-Embedded ECG EES and PPG EES System in the Neonatal Intensive Care Unit 1 41 Hispanic 2 34 South Asian 3 40 Caucasian 4 39 African American 5 36 African American 6 35 Caucasian 7 41 Caucasian 8 38 South Asian 9 37 Caucasian 10 38 Caucasian 11 34 Caucasian 12 34 Caucasian 13 40 Caucasian 14 33 Caucasian 15 33 Caucasian 16 28 Hispanic 17 36 African American 18 39 African American

TABLE 2 Estimation of the costs of the ECG EES and PPG EES. Component Cost Determination Passive Components $0.30 per sensor given about 30 passive components per device at $0.01 per passive component Active Components $3.79 per RF unit $3.19 for the instrumentation amplifier (only ECG EES) $4.7 for photodiode/LEDs/rectifier/buck converter (only PPG EES) $1.25 for the voltage feedback amplifier Silicon PDMS $127.64 for 100 devices Encapsulation (10 g/device) ($63.82/0.5 kg) (PDMS, Silbione) Silbione $88.10 for 100 devices High Tack Silicone (5 g/device) ($39.95/8 oz) Gel. A-4717-1 Subtotal: $215.74 for 100 devices/$2.16 per device Ionic Liquid $2.58 per devices (0.7 g of ionic fluid per device) Dual Copper Sheet $4.60 per device ($947/50 Sheets) Cleanroom ($18/hr) $180 for 100 devices (10 devices/hr) Fabrication Costs Harrick Plasma Cleaner $475 for 100 devices (Photolithography, ($19/hr) (4 devices/hr) E-beam, RIE) Subtotal: $6.55 per device Total $17.96 (ECG EES)/$19.47 (PPG EES) per device

The battery-free, wireless power transfer strategies described here offer advantages in form factor for extremely low birth weight neonates less than 27 weeks of gestational age, although the device requirements for proximity to a primary antenna is less than ideal. Strategies that implement small batteries for operation when wireless power is unavailable, or those that exploit multiple primary antennas can be pursued. The devices may further integrate additional sensors to measure parameters such as transcutaneous CO₂ and O₂, ballistocardiography, motion and crying time.

The NICU represents one of the most challenging environments to develop new medical technologies given the extreme fragility of the population, and the high acuity of care. The results reported here follow from a collection of advances in engineering science, to establish the basis for a wireless, skin-like technology that not only reproduces comprehensive vital signs monitoring capabilities currently provided by invasive, wired systems but that also adds multi-point sensing of temperature and continuous tracking of blood pressure. These sensors explicitly address the unique needs of the NICU due to their high mechanical compliance and non-invasive skin adhesive interface, their water resistance, and their compatibility with essential medical imaging and inspection. Further clinical validation and testing may lead to broad adoption in both high-resource and low-resource settings.

Fabrication: the fabrication involves a combination of semiconductor processing steps, lamination procedures, transfer printing processes and chip placement and solder bonding. Addition of a thin layer of PDMS layer bonded around the perimeter of the device and the electrodes allowed filling with an ionic liquid using a syringe to form the microfluidic channel. A coating of a soft silicone material on the bottom layer provides a light adhesive surface.

Sensor assessment: the primary antenna (size of 32 cm×34 cm; FIGS. 22A-22B) connected to the host system for simultaneous transfer of RF power to the ECG EES and the PPG EES. The low current consumption of these platforms (about 450 μA and 5 mA as peak current, respectively) can be satisfied by RF power (5 W; compliant to EN 50364; standard for human exposure) at vertical distances of up to 25 cm through biological tissues, bedding, blankets, padded mattresses, wires, sensors and other materials found in NICU incubators, and across lateral areas of 32 cm×34 cm, for full coverage wireless operation in a typical incubator.

The primary antenna was pre-embedded within existing NICU incubators. Sensors were placed on the skin without skin preparation for the neonate thereafter. Data was transmitted, collected, and stored for further data analysis on a table PC (e.g., Surface Pro 4, Microsoft®).

Fabrication of the Metal Coil and Interconnectors and the Microfluidic Channel

A double layered copper (Cu) foil (18/5 μm thick, Oak Mitsui MicroThin Series) provided the material for the NFC coil and interconnectors (FIGS. 8A-8B). After lamination of this Cu foil onto the PDMS (Sylgard 184, Dow-Corning; 10:1 weight ratio) coated glass slide, with the 5 μm thick Cu side down and 18 μm side up, the Cu foil was peeled off by hands. The NFC coil and interconnectors was micro-patterned by photolithography (photoresist AZ P4620, AZ Electronic Materials; spin-casting at 3000 rpm for 30 sec, soft baking on a hot plate at 110° C. for 3 min, UV irradiance for 500 mJ/cm², and development for about 50 sec with developer AZ 400K/DI water solution of 1:3 volume ratio), and wet etching (CE-100 copper etchant, Transense; about 2 min with frequent rinsing by DI water). Photoresist was removed with acetone, IPA, and DI water rinse. After the native Cu oxide on the surface was eliminated by using oxide remover (Flux, Worthington), electrical circuit components were assembled with indium/silver soldering paste (about 130° C., 1 min). The whole area of the ECG EES and PPG EES was encapsulated by a low modulus silicone elastomer after the second metal layer (e.g., bridge and red/IR LED part), the back side insulated by a thin PDMS coating, was connected with the first metal interconnectors.

For the microfluidic channel, photolithography defined SU-8 mold (photoresist SU-8 2100, MicroChem; spin-casting at 3000 rpm for 30 sec, soft baking on a hot plate at 65° C. for 3 min and 95° C. for 20 min, UV irradiance for 380 mJ/cm², post exposure baking on a hot plate at 65° C. for 3 min and 95° C. for 10 min, development for about 20 min with SU-8 developer, IPA rinsed, and hard baking at 120° C. for 30 min). Spin-casting polytetrafluoroethylene (PTFE, Sigma-Aldrich; thickness of about 100 nm) at 3000 rpm for 30 sec and baking at 110° C. for 5 min formed a thin antiadhesive layer on the SU-8 mold. An additional spin casting on top of the mold and curing at room temperature for 24 hours yielded a bottom PDMS (Sylgard 184, Dow-Corning; 10:1 weight ratio) substrate. Delamination from the SU-8 mold allowed sample placement on a glass substrate with the feature side facing up. Next, a thin film of a fluoropolymer (1 μm, OSCoR 2312 photoresist solution, Orthogonal INC) spincast on a PDMS substrate and then thermally annealed (50° C. for 1 min) yields a low energy coating.

After exposure to oxygen plasma generated at low power (8.5 W) RF at 500 mTorr (Plasma Cleaner PDC-32G, Harrick Plasma) for 20 sec, the upper part (electronic layer encapsulated by PDMS) and the lower part (thin PDMS layer with microfluidic channel) was aligned and bonded. Finally, the bottom side was covered with a Silbione layer and a syringe with a micro-needle injected a blended solution (82:18, volume ratio) of ionic liquid (1-ethyl-3-methylimidazolium ethyl sulfate [EMIM][EtSO₄], Sigma-Aldrich) and silica gel (high-purity grade, pore size 6 nm, 200-425 mesh particle size, Sigma-Aldrich) into the microfluidic channel.

Mechanical Simulations

The commercial software ABAQUS (ABAQUS Analysis User's Manual 2010, V6.10) was used to study mechanics of the devices and to optimize the design layouts. The objectives are to ensure that (1) the interfacial normal and shear stresses on the skin are below the low somatosensory perception of the device on the human skin; and (2) the strain in the copper layers is below the elastic limit such that no plastic yielding occurs. The PDMS (elastic modulus 500 kPa and Poisson's ratio 0.5), Silbione (elastic modulus 3 kPa and Poisson's ratio 0.5) and ionic liquid were modeled by hexahedron elements (C3D8R) while the stiff copper (elastic modulus 119 GPa and Poisson's ratio 0.34) film was modeled by composite shell elements (S4R). The positions of the chips and the widths of serpentine interconnects were optimized to satisfy the competing requirements from mechanics and electromagnetical designs. For example, narrow interconnects improve the elasticity stretchability, but lead to the undesired increase in the electrical resistance. An iterative optimization process was adopted to carefully balance these competing requirements and other mechanical and electromagnetical considerations. The positions of the chips were optimized to avoid entanglement of interconnects and contact between components. The minimum work of adhesive Gmin required to prevent device delamination from the stretched skin was also shown in FIG. 35. For stretching less than 20%, Gmin is small such that the van der Waals force between the devices and skin is enough to provide this adhesion (16 N/m), i.e., without the need of any adhesives.

Electromagnetic Simulations

A finite element method was used in the electromagnetic simulations to determine the inductance, Q factor and the scattering parameters S11 of the ECG EES and PPS EES in undeformed and deformed states. The simulations were performed using the commercial software Ansys HFSS (Ansys HFSS 13 User's guide, Ansys Inc. 2011), where the lumped port was used to obtain the scattering parameters S11 and port impendence Z. An adaptive mesh (tetrahedron elements) together with a spherical surface (1000 mm in radius) as the radiation boundary, was adopted to ensure computational accuracy. The inductance (L) and Q factor (Q) (shown in FIGS. 9A-9B) were obtained from L=Im{Z}/(2πf) and Q=|Im{Z}/Re{Z}|, where Re{Z}, Im{Z} and f represent the real and imaginary part of the Z and the frequency, respectively. For 20% stretching of the loop antennas of the ECG EES and PPG EES, the changes of the inductance, Q factor and resonant frequency are less than 5% (FIGS. 17A-17C and 18A-18C). For bending radii >about 140 mm for the chest and >about 50 mm for the foot, the inductance, Q factor and resonant frequencies are approximately unchanged (FIGS. 12A-12C and 13A-13C).

Simulation for Peel Test

The commercial software ABAQUS (ABAQUS Analysis User's Manual 2010, V6.10) was also used to study peel force of conventional adhesive (elastic modulus 5 MPa and Poisson's ratio 0.5), and EES adhesive with/without the ionic liquid layer (FIGS. 25A-25C), and with different patterns of holes (FIGS. 27A-27D). The adhesion energy of the interface between the phantom skin and EES/conventional adhesives obtained from experiments were 16 N/m and 175 N/m, respectively. The cohesive strengths σ₀ were estimated as 20 kPa and 50 kPa for the EES adhesive and conventional adhesive, respectively, from FIG. 2E. The peeling velocity was 0.53 mm/s, from experiments. The cohesive zone model is shown in FIG. 23.

Simulations of Electromagnetics Associated with MRI Imaging

The finite element method was used to determine the magnetic fields. The simulations were performed using a commercial software (Ansys HFSS 15 User's guide, Ansys Inc. 2012), where adaptive mesh (tetrahedron elements) together with a spherical surface (2000 mm in radius) as the radiation boundary, was adopted to ensure computational accuracy. The in-plane gradient of the magnetic field density underneath the electrodes (FIGS. 3A and 3E) was obtained from |∇pB|=[(∂B/∂x)²+(∂B/∂y)²]^(1/2) and |∇_(z)B|=|∂B/∂z| with a working frequency of 128 MHz, where B is the magnitude of the magnetic field density, and x, y, z, are the orthogonal coordinates of in the electrode plane.

Simulations for Thermal Load of EES Sensors

The commercial software ABAQUS (ABAQUS Analysis User's Manual 2010, V6.10) was used to study the temperature change of the skin for one-time MRI scan. The oscillating magnetic field density in MRI is B=20 μT, and the working time for one-time scan of MRI is 0.5 ms. The received power of the ECG EES from the electromagnetic simulation is imported into ABAQUS for thermal analysis. The convective heat transfer coefficient of air is 6 W/(m²·K). Except for Cu, the hexahedron elements (DC3D8) were used, whereas thin Cu layer was modeled by the shell elements (DS4). The minimal mesh size was 1/10 of the thickness (10 μm) of the ionic layer, and the mesh convergence of the simulation was ensured. The thermal conductivity, heat capacity and mass density used in the simulations are 0.35 W·m⁻¹·K⁻¹, 2135 J·kg⁻¹·K⁻¹ and 1490 kg·m⁻³ for the skin; 0.15 W·m⁻¹·K⁻¹, 1510 J·kg“¹·K⁻¹ and 1000 kg·m⁻³ for PDMS; 0.15 W·m⁻¹·K⁻¹, 2200 J·kg”¹·K⁻¹ and 1100 kg·m⁻³ for ionic liquid; 0.15 W·m⁻¹·K⁻¹, 1460 J·kg⁻¹·K⁻¹ and 970 kg·m⁻³ for Silbione; and 386 W·m⁻¹·K⁻¹, 383 J·kg¹·K⁻¹ and 8954 kg·m⁻³ for Cu, respectively.

Example 2 Advanced Physiological Monitors for Neonatal Care

The apparatuses and methods provided herein have applications including, but not limited to: critical care monitoring in neonatal intensive care units; critical care monitoring in pediatric intensive care units; critical care monitoring in neonatal/pediatric cardiac care units; critical care monitoring in neonatal/pediatric neocritical care units; post-discharge home monitoring for high-risk neonates; critical care monitoring in adults; home monitoring for medical recovery; and monitoring for rehabilitation care.

The advantages of the apparatuses and methods include foundational concepts of skin-like, multi-modal sensors enabled by advances in in-sensor analytics and time-synchronized, multi-nodal wireless operation. This offers the ability to significantly improve the efficacy and safety of vital signs monitoring for newborns in neonatal intensive care units.

Ultra-low noise operation enables capture of low-power physiological signals such as fetal heart rate or miniscule movements of the chest wall reflective of breathing in a premature neonate.

Apparatuses may include two separate but software linked (e.g., “electronically-coupled”) sensor systems: a chest-deployed unit with ECG, skin temperature, and seismocardiograhy, and a limb-based unit with photoplethysmography for pulse oximetry.

Further embodiments include the deployment of multiple sensors at various locations dependent on the clinical use case. For instance, during skin-to-skin or “kangaroo care” where a baby is placed on the mom's chest, the ECG sensors can be placed on the back or flank of the neonate.

Advanced software function and interoperability enabling cloud storage, remote login, and secure communication. Further capabilities include the integration of third-party sensors, wearables, and other hardware systems.

Design features that enable immediate deployability in NICUs include: Radiolucency that is compatible to CT and XR imaging; MRI compatibility; and optically transparent design allows for clinical evaluation of the skin directly beneath sensor negating the need for removal that can be damaging to fragile skin.

Safety features that drastically decrease the risk of iatrogenic injury and support therapeutic skin-to-skin contact include: The soft, mechanical nature of the sensor itself enables intimate skin coupling without the need of powerful adhesives. The removal of traditional electrodes and sensors with adhesives lead to skin stripping and iatrogenic injuries including permanent scarring. The devices and systems provided herein exhibit peel forces orders of magnitude lower than existing systems. Soft, thin, wearable nature allows for skin-to-skin contact that is unobstructed between mother and baby.

Advanced physiological monitoring capabilities that exceed current standard of care capabilities includes: continuous measurement of skin temperature at multiple locations of the neonate; thus, this allows for the development of novel metrics of peripheral perfusion; lows for calculation of pulse arrival time and pulse transit time—these measures are surrogate markers of blood pressure but can be measured continuously and non-invasively. A high-frequency 3-axis accelerometer within the sensor system can be placed directly on the chest enabling continuous, wearable seismocardiography (SCG) of neonates. This enables continuous recording of heart sounds, and assessment of chest wall movements with breathing for more accurate respiratory rate. The apparatuses may enable correlation of SCG with stroke volume and ejection fraction measured by echocardiography. The accelerometer also allows analysis of a baby's position including when a baby is upright. This can be used to quantify important parameters such as how long a baby is being held for kangaroo care, being fed, resting, crying and the like. The output of the sensor can be used to determine whether a baby has sustained an injury that is consistent with non-accidental trauma (e.g., child abuse).

The multi-nodal (and multi-modal) aspect of the devices provided herein facilitate at least dual measurement systems to capture accurate respiratory rate. The measurement of respiratory rate derived through the ECG via impedance pneumonography is often times inaccurate and overestimates the true respiratory rate. Herein, we describe the ability to measure chest wall movement to derive respiratory rate along with traditional impedance pneumonography.

Each sensor system may have a form factor in a patch-like geometry that occupies a small surface area (less than 2.0 cm×4.0 cm) that facilitates placement on a premature neonate.

Embodiments include: where the form factor includes a single chest unit sensor with all electronics and vital sign monitoring functionality; where the electrode spacing or sensor elements are adjustable; the ability to create alarms based on pre-programmed or physician specified inputs. These alarms include both visual and audio notifications. These notifications can be displayed on an external display unit or onboard the sensor itself (either via an onboard LED or sound).

A sensor system having an optical unit for the photoplethysmograph may be located on the infant's nail (toenail or fingernail).

The sensors may be wrapped circumferentially around a limb or body structure and fastened with a mechanical mechanism (e.g., hook in loop, clasps, buttons, magnets).

Embodiments include where the pulse oximeter unit is placed on various locations of the body to derive a measure location specific pulse oximetry. Locations include, but are not limited to, all 4 limbs, chest, back, abdomen, forehead.

Embodiments include where the same power management and antennae schema is applied to Bluetooth rather than NFC.

Embodiments include the sensors having an onboard battery—but wireless charging is implemented in instances where a wireless power source is detected which simultaneously powers the sensor and charges the battery.

Here we report foundational concepts for a wireless, battery-free vital signs monitoring system that exploits an at least bi-nodal pair of ultrathin, low-modulus measurement modules, each referred to here as an epidermal electronic systems (EES), capable of gently and non-invasively interfacing onto the skin of neonates, even at gestational ages that approach the limit of viability. The materials choices and device architectures leverage the most advanced concepts in soft electronic systems, with modes of operation that follow from four essential advances reported here: (1) techniques for simultaneous wireless power transfer, low noise sensing and data communications via a single link based on magnetic inductive coupling at a radio frequency band that has negligible absorption in biological tissues, (2) efficient algorithms for real-time data analytics, signal processing and dynamic baseline modulation implemented in the highly constrained computing resources available on the sensor platforms themselves, (3) strategies for time-synchronized, continuous streaming of wireless data from two, separately located devices and (4) fully transparent and radiolucent designs that enable visual inspection of underlying tissue of the skin interface, and magnetic resonance (MRI) and X-ray imaging (XR) of the neonate. The resulting systems are qualitatively smaller in size, lighter in weight and less adhesive to the skin than clinical standard hardware, with potential for costs that are orders of magnitude lower. Other embodiments of the sensor include the coupling of Bluetooth communication and small embedded batteries.

FIG. 1B presents schematic representations of the two wireless, EES that, when used together in a time-synchronized fashion, constitute an overall bi-nodal platform capable of reconstructing full vital signs information. The electronic layer in each EES incorporates a collection of thin, narrow serpentine metal traces (Cu, 50-100 μm in width, 5 μm in thickness) that interconnect multiple, chip-scale circuit components, including passives (resistors, capacitors, inductors) and actives (infrared and red light emitting diodes (LEDs), photodiodes (PDs), system-on-a-chip (SoC) components with power harvesting, radio frequency (RF) communication, microcontroller, analog-to-digital conversion and general input/output functionality). One EES mounts on the chest to record electrocardiograms (ECGs; FIG. 1B top panel) through skin-interfaced electrodes that consist of filamentary metal mesh microstructures in fractal geometries; the other mounts on the base of the foot to record photoplethysmograms for pulse oximetry (PPGs; FIG. 1B bottom panel) by reflection mode optical measurements. A microfluidic chamber filled with a non-toxic ionic liquid (1-ethyl-3-methylimidazolium ethyl sulfate [EMIM][EtSO₄], Sigma-Aldrich) between the electronics and the lower encapsulation layer mechanically strain-isolates the system from the fragile skin of the neonate. In addition to the electronics, each EES incorporates a magnetic loop antenna (inductance, Q-factor, and S11 at 13.56 MHz are 3.88 μH, 10.65, and −26.54 for the ECG module and 0.84 μH, 7.12, and −23.07 for the PPG module, respectively) tuned to compliance with NFC protocols, and configured to allow simultaneous wireless data transmission and wireless power delivery through a single link. The low conductivity of the ionic liquid allows stable electrical operation in this RF environment. The resulting bi-nodal system captures and continuously transmits ECG, PPG and skin temperature (from each EES), HR, heart rate variability (HRV), RR, SpO₂ and a surrogate of systolic blood pressure (BP), as discussed subsequently.

The images shown in FIG. 1C highlight the overall size and the ultrathin, soft form factor of these systems. Stretching the ECG EES uniaxially by up to 15% (FIG. 1D) induces interfacial normal and shear stresses on the skin that lie below the threshold for human sensation (about 20 kPa). Similarly low levels of stress result from stretching of the PPG EES up to 13%. In both cases, deformations result in strains in the electronics and antenna structures that are beneath the limits for plastic deformation (about 0.3%). The thin geometry, exceptionally low modulus mechanics and minimal interfacial stresses enable reliable coupling to the skin of the neonate based on weak, van der Waals forces alone, thereby eliminating the need for skin adhesives. FIG. 1E shows pictures of the PPG EEG with red LED activated, captured with and without external illumination.

Because the standard NFC protocol at 13.56 MHz supports only low speed, low fidelity applications in contactless payments, wireless identification and others, significant optimization is necessary in both the transponder and host reader systems at ISO15693 to enable required data transfer rates for NICU monitoring (hundreds of Hz). These optimizations enable continuous streaming of data at rates of up to 800 bytes/s with dual channels, which is orders of magnitude larger than previously reported NFC sensing devices and represents a first example of bi-nodal, time-synchronized operation. A key is in minimizing the overhead associated with transfer by packaging data into 6 Blocks (24 Bytes) in a circular buffer. Here, reading occurs with an NFC host (LRM1002, Feig Electronics) interfaced to a microcontroller (MCU, ARM® Cortex™-M4F) in a Bluetooth Low Energy (BLE) system (SoC, nRF52832, Nordic Semiconductor) configured this type of customized circular buffer decoding routine. The receiver antenna (size of 32 cm×34 cm) connects to the host system for simultaneous transfer of RF power to the ECG EES and the PPG EES. The low current consumption of these platforms (about 450 μA and 2 mA as peak current, respectively) can be satisfied by RF power (5 W; compliant to EN 50364; standard for human exposure) at vertical distances of up to 25 cm, through biological tissues, bedding, blankets, padded mattresses, wires, sensors and other materials found in NICU isolettes, and across lateral areas of 32 cm×34 cm, for full coverage wireless operation in a typical incubator. The BLE radio allows transmission of data to a personal computer, tablet computer or smartphone with a range of up to 20 m. Further software embodiments would enable direct communication and telemetry with legacy systems in the NICU including electronic medical records.

In-sensor processing and data analytics further reduce bandwidth requirements on wireless transmission and greatly improve the robustness in operation. For example, computational facilities on the NFC SoC of the ECG EES can support a streamlined version of the Pan-Tompkins algorithm for accurate, on-board analysis of the QRS complex of ECG signals in real-time to yield HR, HRV, and RR on a beat to beat basis. FIG. 50A summarizes an approach that starts with a finite impulse response (FIR) digital bandpass filter (fc1=5 Hz, fc2=15 Hz) to attenuate the noise outside the passband. Differentiating and squaring the resulting data yields the slope of QRS peaks and prevents false peak detection associated with the T wave. Applying a moving average (N=30) and a dynamic threshold identifies a running estimate of the R peak and the magnitude of the noise. Automatic adjustments of the threshold rely on these estimates for the preceding beat cycle. The R to R intervals determined in this way yield the instantaneous HR. Simultaneous recordings obtained using a clinical standard system, henceforth referred to as ‘gold’ standard data, validate the ECG module hardware and in-sensor analytics, per measurements on a healthy adult volunteer (FIGS. 50B-50C). The ECG signals and computed HR values from these two platforms show no measurable differences. Periodic modulations of the amplitude of the R peak define the RR (FIG. 50D), which also agrees with the gold standard (visual counting by a physician in this case; FIG. 50E).

Measurements of skin temperature rely on sensors internal to the NFC SoC in each EES, where transmission at a sampling frequency of 1 Hz is sufficient for monitoring purposes. The exceptionally low thermal mass of the EES and the small thickness of the substrate layer (PDMS; 50 μm in thickness) that separates the SoC from the skin ensure fast thermal response times and excellent thermal coupling, respectively. Comparisons against readings from an FDA-approved thermometer serve as means to calibrate the sensor (FIG. 50F) via testing in a water bath. Thermal images captured with an IR camera (FLIR A325SC, FLIR Systems) during operation indicate negligible heating associated with the electronics or the antenna structures (FIG. 50G). FIG. 50H shows temperature readings from ECG EES for 60 seconds after calibrated against thermometer. Simultaneous measurements of temperature on the chest and foot, which follow naturally from the bi-nodal nature of the system, can be clinically important as described subsequently.

The PPG EES relies on similar NFC protocols, but with in-sensor analytic methods that not only reduce requirements on transmission bandwidth but also provide, when used in conjunction with adaptive circuits, crucial functionality for stable operation. Specifically, the processing in this case enables (i) dynamic baseline control to ensure that the input to the ADC on the NFC SoC lies within the linear response range and (ii) real-time calculation of SpO₂ from the PPG traces (FIG. 51A). Here, the processing begins with application of a moving average filter (N=15; 100 ms) to the photodetector response from the red and IR LEDs. When the larger of these two averaged PPG amplitudes, typically that associated with the IR response, lies outside boundary at the voltage of 0.2 V and 0.7 V, a programmable difference amplifier (FIG. 51B) with voltage dividers at V+ dynamically controls the baseline level according to:

V _(tr) =−Z _(f) i _(PD)+(1+Z _(f) /R _(s))V ₊ =−R _(f)/((

jwR

_(f) C _(f)+1))i _(PD)+(1+R _(f) /R _(s))V ₊  (4)

where V_(tr) is output of the amplifier, Z_(f) is impedance of feedback loop, R_(s) is series resistance, C_(f) is feedback capacitor, R_(f) is feedback resistor, i_(PD) is current output of photodiode and,

V ₊ =

V _(dd) R

_(d2)/(R _(d2) +a2(4R _(g) +R _(d1))+a1(2R _(g) +R _(d1))+a0(R _(g) +R _(d1))).  (5)

Four different baseline levels can be accessed via activation of three GPIO outputs (a0, a1, a2). FIG. 51C shows dynamic control of the output voltage (VADC) of a sinusoidal input signal (frequency=50 mHz, amplitude=35 mV, V_(offset)=−30 mV). Starting with the default setting (LV3), the baseline level automatically adjusts to lower levels associated with VADC above the boundary, and vice versa with VADC below it, thereby maintaining VADC in an allowed range. FIG. 51D summarizes the operation in an actual PPG recording. Without this type of real-time, in-sensor processing (IR_(Non) in FIG. 51D) robust operation would be impossible: PPG signals would quickly drift outside of the narrow operating range of the ADC due to patient-to-patient variations in skin pigmentation and unavoidable, time-dependent fluctuations in optical scattering that result from micromotions relative to underlying blood vessels and subdermal structures.

Calculating SpO₂ involves determining the ratio (R_(oa)) between the alternating component and the direct component of PPG signals according to the following equation

R _(oa)((

AC

_(RED))/

DC

_(RED))/(

AC

_(IR) /

DC

_(IR))  (6)

for data from the red and IR LEDs (FIG. 51E). A peak detection algorithm plays a central role in determining the peak and valley points for accurate calculation of R_(oa). Peaks and valleys correspond to the locations at which the slope turns from positive to negative and vice versa, respectively. A 200 ms refractory period imposed after detection of a peak prevents false negatives from the dicrotic notch feature characteristic of normal PPG waveforms. An empirical calibration formula determined by comparison to a gold standard measurement (MightySat Fingertip Oximeter, Masimo) converts the R_(oa) to SpO₂ (FIG. 51F). Time dependent variations of SpO₂ determined in this manner appear in FIG. 51G. The rapid drop and recovery result from a breath hold.

The time synchronized outputs from the ECG EES and the PPG EES allow determination of the pulse arrival time (PAT), as defined by the time lapse between the maximum fiducial point in the ECG signal (R peak) and the corresponding minimal fiducial point in the PPG signal at valley as in (FIG. 51H). Literature studies support a quantitative correspondence between PAT and systolic BP. Specifically, the Moens-Korteweg equation provides a linear relationship between PAT and BP. For real-time data analysis, processing of ECG and PPG data in the host (i) time-stamps each wirelessly transmitted data point with the local clock of each EES, where these local clocks sync with a global clock based on the high-frequency clock of the BLE SoC, thereby providing time synchronization (ii) applies a cubic spline interpolation to the ECG and PPG data to obtain an equivalent 1 kHz version for improved timing accuracy, (iii) computes time differences to yield PAT values for each beat cycle and (iv) imposes a moving average on these PAT values over a 1-minute period to reduce the noise. Measurements of 1/PAT performed in this manner, together with corresponding values of systolic BP captured using a sphygmomanometer on a healthy subject during a period of rest after exercising (running at 6 miles per hour for 15 minutes), exhibit the expected linear relationship (FIG. 51I). A calibration plot with a linear fit appears in FIG. 51J.

A full demonstration of the wireless bi-nodal system on a neonate (38 wks 3/7, 2.75 kg) validates the performance a clinical environment. Here, the NFC antenna for power transfer and data communication lies beneath the mattress inside an incubator (FIG. 6A). An ECG and a PPG EES softly mount on the chest and the dorsum of the foot, respectively, where van der Waals forces govern the mechanical interface to the skin, with minimal mechanical, mass or thermal load (FIG. 6A). FIG. 6B demonstrates use in a mode that facilitates skin-to-skin contact between parent and child, as a form of therapeutic touch that is nearly impossible to replicate with hard-wired conventional systems. FIG. 6C shows an alternative location of an ECG EES on the back of a neonate to demonstrate another mounting locations to promote skin-to-skin interaction. The magnified image in FIG. 6D highlights the intimate contact with the skin while naturally deformed and wrinkled. Results of continuous recordings are in FIG. 6E. FIG. 6E demonstrates deployment of a PPG EES on back of hand for a neonate with dark skin color. Calculated HR, SpO₂, and RR compare favorably against gold standards. The temperature and PAT data appear alone due to the absence of a temperature probe or arterial line during the experiments (FIG. 6G). Sphygmomanometer cuffs represent a direct risk for pressure-related injuries in premature neonates and are highly inaccurate in low-birth weight neonates. Measurements of temperature are typically limited to a single body location due to the need to minimize wired connections and adhesive interfaces to the skin. The bi-nodal configuration of the system presented here naturally yields not only a surrogate marker of BP but also temperatures at two different locations (trunk and limb), to improve monitoring for hypothermia and provide a noninvasive method to track peripheral perfusion. Additional demonstrations in the NICU with related devices indicate similar performance on neonates with gestational ages as low as 28 weeks and weights as low as 1470 g.

FIG. 52A demonstrates important user-centric design aspects that enable the ECG EES and PPG EES to operate seamlessly within NICUs. The greatest risk of skin stripped is secondary to adhesives removal of electrodes—our experimental results suggests that the van der Waals adhesion forces that still allow for intimate skin coupling are 20 times weaker than those associated with conventional NICU adhesives (FIG. 52B). The drastically lower peel forces associated with the removal of the ECG EES and PPG EES presented here would dramatically reduce the risk of skin-related iatrogenic injuries. Medical imaging, and direct nursing and physician evaluation of skin integrity are standard, essential procedures in the NICU. The optical transparency provides nurses and physicians with direct visual access to the skin and tissue beneath the sensor (FIG. 6D) without the need for removal as a routine means to examine for signs of infection or skin breakdown. The elimination of wires, which are radiopaque, improves the evaluation of X-ray images, which are required for 90% of low-birth weight neonates. MRI-compatibility is an additional important design consideration, as this imaging modality enables precise assessment of white matter, gray matter, and posterior fossa abnormalities, with functional capabilities that exceed those of ultrasound. FIGS. 52C-52D show the MRI images in sagittal and axial planes, respectively. When the ECG EES is placed overlying cadaveric chicken tissue in a clinical MRI system (7 T MRI Bruker PharmaScan MRI system), there were no observable magnetically induced displacement force and torque, or measurable levels of RF-induced heating—these features are required by the FDA to enable an “MRI-safe” label. (Adding information for X-ray and CT in the future). The encapsulation within a silicone elastomer enables operation even when completely immersed in water—this allows for full functionality when operating in a neonatal incubators that are commonly set at >80% humidity or higher to maintain temperature homeostasis and prevent dehydration in premature neonates.

A hardware modification for further enhancement in functionality including 6-axial inertial movement unit (IMU; 3-axial accelerometer and 3-axial gyroscope; BMI160, Bosch Sensortec), a Bluetooth SoC with 32-bit ARM Cortex-M4F microprocessor (nRF52832, Nordic Semiconductor), and on-board flash memory (S25FS512, Cypress). FIG. 1I shows the schematic of the hardware modification. The IMU unit enables seismocardiography on the chest when deployed in the ECG EES, thereby providing mechano-acoutic information of the heart including heart sounds for echocardiogram and periodic vibration from breathing for accurate respiratory rate. Deployed in the PPG EES, the IMU serves as a feedback-controlled motion artifact reduction algorithm to compensate the vulnerability of PPG signals being prone to motion artifact. Acceleration and orientation information obtained from two IMUS on the chest and foot, respectively, provides posture information of baby. The posture pattern accessed from the IMU is further analyzed through machine learning based algorithm to identify Kangaroo Mother Care (KMC). The ECG EES also enables maternal/fetal measurement from both fetal electrocardiography (fECG) and mechano-acoustic movement of fetus. The algorithm for fECG extraction is based on singular value decomposition that compares the pattern weights in raw ECG signal. The maternal ECG corresponds to the greatest weight, while the fetal ECG the second greatest. After identifying peaks of maternal ECG (mECG) and weight pattern is obtained by singular value decomposition, fECG can be isolated by removing components having the greatest pattern values. Mechano-acoustic movement of fetus can also give fetal heart rate (fHR).

While certain embodiment of the sensor systems are purely wirelessly powered, other embodiments of the sensor systems with onboard power when a neonate or infant is moved away from the inductive antennae are disclosed. Furthermore, a hardware modification is also disclosed to include a secondary power supply plan using a small battery embedded in the sensors through power supply and management units with three mechanisms: (1) charging battery when wireless power transfer (WPT) is activated, sensed through WPT sensing circuit, (2) activating primary power source through WPT that continuously supplies power to the sensors via full wave rectifier and voltage regulator, (3) activating secondary power supply based battery when wireless power transfer is not sensed. Extremely low-power nature of our sensors is achieved by optimizing power management using both on-board memory and down-sampled real-time wireless transmission such that the raw data is stored into flash memory while power demanding real-time transmission event is effectively duty cycled to minimized power consumption without loss of signal quality. The outcome is facilitating 24-hour battery power operation using small non-magnetic embedded battery (12 mAh, 9 mm×9 mm×3 mm (W×L×H)) without affecting the overall dimension or thickness of the sensor significantly.

FIG. 53 shows the underlying software enables interoperability with third party platforms, according to one embodiment of the invention. Further capabilities include cloud storage in a HIPAA complaint manner. The receiver may be a tablet, smartphone, or existing vital signs monitor.

Also, further software innovations to the sensor systems according embodiments of the invention distinguish this invention from prior works. Currently, the wireless sensors each communicate via Bluetooth Low Energy (BLE) with mobile devices (e.g., Microsoft® SurfacePro and Samsung® smartphones). Software enables continued transmission of captured data to a cloud-based server. The cloud will decouple a neonate's data from the mobile devices by centralizing the data with an HIPAA-compliant data storage (Amazon Simple Storage) and database (Amazon Relational Database). It will also provide opportunities to integrate with existing systems including Electronic health record (EHR) and Hospital information system (HIS) with GE Healthcare MUSE eDoc Connect. By utilizing the cloud's computation nodes with General-purpose computing on graphics processing units (GPGPU) and Field-programmable gate array (FPGA), the platform can perform accelerated real-time analytics and machine learning, and provide a base to do distributed computation on cloud clusters with big-data engines such as Apache Spark. By developing interfaces to the server via Representational State Transfer (REST) Application programming interface (API) and web interface, authorized doctors and researchers will have a secure remote access to the data and tools to execute post-hoc analysis. Relevant parameters for in-clinical care use include 24-hour battery power operation, cloud integration, and a web-interface.

FIG. 54 shows an example of a user interface, according to one embodiment of the invention. Wireless wearable sensors that are discoverable are shown on the left panel. Beyond the sensors themselves, our user interface and base displays can also be used to deliver therapeutic benefit. For instance, musical therapy has been shown to be beneficial to neonatal brain development and neonatal stress relief. Existing displays and monitoring systems are only capable of alarms. Also available on the user interface is an avatar that can depict the patient position, such as on the back, side or front.

The foregoing description of the exemplary embodiments of the present invention has been presented only for the purposes of illustration and description and is not intended to be exhaustive or to limit the invention to the precise forms disclosed. Many modifications and variations are possible in light of the above teaching.

The embodiments were chosen and described in order to explain the principles of the invention and their practical application so as to activate others skilled in the art to utilize the invention and various embodiments and with various modifications as are suited to the particular use contemplated. Alternative embodiments will become apparent to those skilled in the art to which the present invention pertains without departing from its spirit and scope. Accordingly, the scope of the present invention is defined by the appended claims rather than the foregoing description and the exemplary embodiments described therein.

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1. An apparatus for measuring physiological parameters of a mammal subject, comprising: a first sensor system and a second sensor system that are time-synchronized to each other, each of the first sensor system and the second sensor system comprising: a plurality of electronic components, and a plurality of flexible and stretchable interconnects electrically connecting to different electronic components, wherein the plurality of electronic components comprises a sensor member for measuring at least one physiological parameter of the mammal subject, a system on a chip (SoC) having a microprocessor coupled to the sensor member for receiving data from the sensor member and processing the received data, and a transceiver coupled to the SoC for wireless data transmission and wireless power harvesting; and an elastomeric encapsulation layer at least partially surrounding the plurality of electronic components and the plurality of flexible and stretchable interconnects to form a tissue-facing surface and an environment-facing surface, wherein each of the first sensor system and the second sensor system is attached to a respective position on the mammal subject so that the first sensor system and the second sensor system are spatially separated by a distance.
 2. The apparatus of claim 1, wherein the distance between the first sensor system and the second sensor system is adjustable between a minimal distance and a maximal distance.
 3. The apparatus of claim 1, wherein the plurality of flexible and stretchable interconnects comprise at least one of serpentine interconnects and zigzag interconnects.
 4. The apparatus of claim 1, wherein the SoC comprises at least one of a near-field communication (NFC) interface and a Bluetooth interface.
 5. The apparatus of claim 1, wherein said transceiver comprises a magnetic loop antenna tuned to compliance with the NFC protocol and configured to allow simultaneous wireless data transmission and wireless power harvesting through a single link.
 6. The apparatus of claim 1, wherein the plurality of electronic components of each of the first sensor system and the second sensor systems further comprises a battery for provide power to said sensor system, and the elastomeric encapsulation layer is configured to electrically isolate the battery from the mammal subject during use.
 7. The apparatus of claim 6, wherein the battery is a rechargeable battery operably rechargeable with wireless recharging.
 8. The apparatus of claim 6, wherein the plurality of electronic components of each of the first sensor system and the second sensor system further comprises a failure prevention element that is a short-circuit protection component or a battery circuit to avoid battery malfunction.
 9. The apparatus of claim 4, wherein the plurality of electronic components of each of the first sensor system and the second sensor system further comprise a power management unit electrically coupled between the SoC and the transceiver.
 10. The apparatus of claim 1, wherein each of the first sensor system and the second sensor system further comprises a microfluidic chamber positioned between the tissue-facing surface and the plurality of electronic components configured to mechanically isolate the plurality of electronic components from a skin surface during use.
 11. The apparatus of claim 10, wherein the microfluidic chamber is at least partially filled with at least one of an ionic liquid and a gel.
 12. The apparatus of claim 10, wherein the encapsulation layer comprises channels or conduits configured to facilitate sweat evaporation during use.
 13. The apparatus of claim 1, wherein the encapsulation layer is optically transparent so as to be compatible with visual inspection of underlying tissue.
 14. The apparatus of claim 1, wherein the encapsulation layer is configured to electrically isolate each of the first sensor system and the second sensor system from an electroshock applied to the mammal subject.
 15. The apparatus of claim 1, wherein the encapsulation layer comprises a flame retardant material.
 16. The apparatus of claim 1, wherein each of the first sensor system and the second sensor system is radiotranslucent and thermally stable so that each of the first sensor system and the second sensor system is compatible with medical imaging.
 17. The apparatus of claim 1, wherein each of the first sensor system and the second sensor system is formed to be stretchable and bendable.
 18. The apparatus of claim 1, wherein each of the first sensor system and the second sensor system is formed in a multi-layer structure to mechanically isolate mechanically stiff components in a mechanical island configuration to accommodate bending, twisting or stretching without fracture or substantial degradation of an operating parameter.
 19. The apparatus of claim 1, wherein each of the first sensor system and the second sensor system is configured to conformally attach to a skin surface in a conformal contact without an adhesive, wherein a contact force is generated by Van der Waals interaction between the tissue facing surface of each of the first sensor system and the second sensor system and a skin surface during use.
 20. The apparatus of claim 19, wherein the adhesive-free conformal contact comprises a wrapped geometry, the sensor member of at least one of the first sensor system and the second sensor system further comprises a fastener connected to an external surface of the encapsulation layer to fasten the sensor member in the wrapped geometry to a mammal subject.
 21. The apparatus of claim 1, wherein each of the first sensor system and the second sensor system further comprises an adhesive layer operably attached to the tissue-facing surface of the encapsulation layer, wherein the adhesive layer has a pattern of perforations through open regions.
 22. The apparatus of claim 1, further comprising a reader system that comprises an antenna in communication with said transceiver of each of the first sensor system and the second sensor system for simultaneous wireless data transmission and wireless power delivery.
 23. The apparatus of claim 22, wherein the reader system further comprises an NFC reader module for receiving wirelessly transmitted data from each of the first sensor system and the second sensor system, and a Bluetooth low energy (BLE) module for transmitting the received data to an external computing device for at least one of real-time display of the monitored physiological parameters, recording of the monitored physiological parameters, and alarm.
 24. The apparatus of claim 1, further comprising an alarm device for providing at least one of an optical alert and an audio alert when a physiological parameter is out of a pre-defined range.
 25. The apparatus of claim 24, wherein the alarm device is at least one of an on-board device and an off-board device.
 26. The apparatus of claim 1, wherein the first sensor system is a conformable torso sensor system configured to attach and conform to a torso region of the mammal subject, and the second sensor system is a conformable extremity sensor system configured to attach and conform to a limb or appendage region of the mammal subject.
 27. The apparatus of claim 26, wherein the torso sensor system comprises: a first electrode and a second electrode as the sensor member; a Bluetooth low energy (BLE) SoC as the SoC; an ECG analog front-end (AFE)/inertial measurement unit (IMU); and a power management integrated circuit (PMIC) and a memory.
 28. The apparatus of claim 26, wherein the sensor member of the torso sensor system comprises at least two electrodes spatially separated from each other by an electrode distance, D, for electrocardiogram (ECG) generation.
 29. The apparatus of claim 28, wherein the electrode distance D is adjustable between a minimal electrode distance, D_(min), and a maximal electrode distance, D_(max), wherein the minimal electrode distance D_(min) is a distance of said two electrodes when the torso sensor system is in a non-stretched state, and the maximal electrode distance D_(max) is a distance of said two electrodes when the torso sensor system is in a maximally stretched state along the distance.
 30. The apparatus of claim 29, wherein the at least two electrodes comprise at least one of mesh electrodes and solid electrodes.
 31. The apparatus of claim 28, wherein the sensor member of the torso sensor system further comprises one or more of: an accelerometer for measuring at least one of a position and a movement; an inertial measurement unit (IMU) for measuring at least one of seismocardiography (SCG) and a respiratory rate; and a temperature sensor for measuring temperature.
 32. The apparatus of claim 26, wherein the extremity sensor system comprises: a Bluetooth low energy (BLE) SoC as the SoC; a PPG analog front-end (AFE); a photodiode/light emitted diode (LED) and an optical detector as the sensor member; and a power management integrated circuit (PMIC) and a memory.
 33. The apparatus of claim 26, wherein the extremity sensor system is configured such that a main circuit component including at least the SoC and the transceiver is aligned and operably wrapped around a limb or appendage in a wrap direction; and the sensor member is spatially separated from and electronically connected to the main circuit component, and operably extends in a direction different from the wrap direction to attach to a sensor region that is spatially distinct from the wrapped portion during use.
 34. The apparatus of claim 33, wherein the sensor member of the extremity sensor system is conformable to a skin surface and configured as a soft wrap for circumferential attaching to the limb or appendage region.
 35. The apparatus of claim 33, wherein the sensor member of the extremity sensor system comprises a photoplethysmogram (PPG) sensor comprising an optical source and an optical detector located within a sensor footprint.
 36. The apparatus of claim 35, wherein the optical light source comprises light emitting diodes (LEDs).
 37. The apparatus of claim 35, wherein the sensor member of the extremity sensor system further comprises one or more of: an accelerometer for measuring at least one of a position and a movement; an inertial measurement unit (IMU) for a motion artifact reduction algorithm; and a temperature sensor for measuring temperature.
 38. The apparatus of claim 1, wherein at least one of the first sensor system and the second sensor system further comprises a dynamic baseline control module configured to automatically compensate for mammal subject-to-mammal subject variability and generate an effective driving current to ensure sufficient signal-to-noise and avoid saturation.
 39. The apparatus of claim 36, wherein the driving current is supplied to an LED to generate an optimized light intensity provided to an underlying mammal subject region.
 40. The apparatus of claim 1, wherein each of the first sensor system and the second sensor system is encapsulated with a thin film of silicone elastomer so that said sensor system is waterproof.
 41. The apparatus of claim 1, wherein each of the first sensor system and the second sensor system has a thickness less than or equal 3 mm.
 42. The apparatus of claim 1, wherein each of the first sensor system and the second sensor system has a Young's modulus less than or equal to 1 GPa.
 43. The apparatus of claim 1, wherein the physiological parameters comprise one or more of a stroke volume and ejection fraction; oxygenation level; temperature; skin temperature differentials; body movement; body position; breathing parameters; blood pressure; crying time; crying frequency; swallow count; swallow frequency; chest wall displacement; heart sounds; core body position; asynchronous limb motion; speaking; and biomechanical perturbation.
 44. An apparatus for measuring physiological parameters of a mammal subject, comprising: one or more sensor systems, each of the one or more sensor systems comprising: a plurality of electronic components and plurality of flexible and stretchable interconnects that are electrically connecting to different electronic components, wherein the plurality of electronic components comprises a sensor member for measuring at least one physiological parameter of the mammal subject, a system on a chip (SoC) having a microprocessor coupled to the sensor member for receiving data from the sensor member and processing the received data, and a transceiver coupled to the SoC for wireless data transmission and wireless power harvesting; and an elastomeric encapsulation layer at least partially surrounding the plurality of electronic components and the plurality of flexible and stretchable interconnects to form a tissue-facing surface and an environment-facing surface, wherein each of the one or more sensor systems is configured to attach and conform to a pre-determined region of the mammal subject, and to be ready time-synchronized with one another.
 45. The apparatus of claim 44, further comprising a reader system that comprises an antenna in communication with said transceiver of each of the first sensor system and the second sensor system for simultaneous wireless data transmission and wireless power delivery.
 46. The apparatus of claim 45, wherein the reader system further comprises an NFC reader module for receiving wirelessly transmitted data from each of the first sensor system and the second sensor system, and a Bluetooth low energy (BLE) module for transmitting the received data to an external computing device for at least one of real-time display of the monitored physiological parameters, recording of the monitored physiological parameters, and alarm.
 47. The apparatus of claim 44, wherein the one or more sensor systems comprises a first sensor system and a second sensor system that are time-synchronized to each other, wherein the first sensor system is a conformable torso sensor system configured to attach and conform to a torso region of the mammal subject, and the second sensor system is a conformable extremity sensor system configured to attach and conform to a limb or appendage region of the mammal subject.
 48. The apparatus of claim 47, wherein the sensor member of the torso sensor system comprises at least two electrodes spatially apart from each other for electrocardiogram (ECG) generation.
 49. The apparatus of claim 47, wherein the sensor member of the extremity sensor system comprises a photoplethysmogram (PPG) sensor comprising an optical source and an optical detector located within a sensor footprint.
 50. The apparatus of claim 48, wherein the sensor member further comprises one or more of: an accelerometer for measuring at least one of a position and a movement; an inertial measurement unit (IMU) for measuring at least one of a movement, a force, an angular rate, and an orientation; and a temperature sensor for measuring temperature.
 51. The apparatus of claim 47, wherein the extremity sensor system is configured such that a main circuit component including at least the SoC and the transceiver is aligned and operably wrapped around a limb or appendage in a wrap direction; and the sensor member is spatially separated from and electronically connected to the main circuit component, and operably extends in a direction different from the wrap direction to attach to a sensor region that is spatially distinct from the wrapped portion during use.
 52. The apparatus of claim 44, wherein the one or more sensor systems comprises three or more sensor systems time-synchronized to each other, wherein at least one of the three or more sensor systems is a conformable torso sensor system configured to attach and conform to a torso region of the mammal subject.
 53. The apparatus of claim 52, wherein at least one of the three or more sensor systems is a conformable extremity sensor system configured to attach and conform to a limb or appendage region of the mammal subject.
 54. The apparatus of claim 1, wherein the mammal subject is a human subject or a non-human subject.
 55. A method for making a sensor system including a plurality of electronic components and a plurality of interconnects electrically connecting to the plurality of electronic components, comprising: forming an elastomeric layer of an elastomeric material on a substrate; forming a first electrically conductive film on the elastomeric layer; lithographically patterning the interconnects in the first electrically conductive film; assembling the plurality of electronic components onto the patterned interconnects; and encapsulating an entire area of the assembled electronic components onto the patterned interconnects with the elastomeric material, followed by detaching from the substrate, to fabricate the sensor system.
 56. The method of claim 55, wherein the elastomeric material comprises PDMS.
 57. The method of claim 55, wherein the electrically conductive film is formed of an electrically conductive material including a metal material comprises Au, Ag, or Cu.
 58. The method of claim 55, wherein said forming the electrically conductive film comprises laminating a double layered film of the electrically conductive material on the elastomeric layer; and removing a top layer of the double layered film.
 59. The method of claim 55, wherein said assembling the plurality of electronic components onto the patterned interconnects comprises connecting a second electrically conductive film for a bridge and a light source to the patterned interconnects.
 60. The method of claim 55, further comprising forming a microfluidic chamber below the plurality of electronic components.
 61. The method of claim 60, wherein said forming the microfluidic chamber comprises attaching a layer of the elastomeric material having the microfluidic chamber defined therein to the bottom surface of the elastomeric layer.
 62. The method of claim 60, further comprising injecting a blended solution of at least one of ionic liquid and silica gel into the microfluidic chamber.
 63. The method of claim 55, further comprising forming a silicone layer on the bottom of the sensor system.
 64. A method of non-invasively measuring physiological parameters of a mammal subject, comprising: conformally contacting a first sensor system at a torso region of the mammal subject and a second sensor system at a limb or appendage region of the mammal subject, respectively, wherein the first sensor system and the second sensor system are spatially separated by a distance, and configured to measuring a torso physiological parameter and an extremity physiological parameter, respectively; and continuously wirelessly transmitting the time synchronized measured torso physiological parameter and extremity physiological parameter to an external reader, thereby non-invasively measuring the physiological parameters of the mammal subject.
 65. The method of claim 64, wherein the distance between the first sensor system and the second sensor system is adjustable between a minimum distance and a maximum distance.
 66. The method of claim 64, further comprising applying a hydrogel between the first sensor system and the second sensor system and underlying tissue of the mammal subject.
 67. The method of claim 64, wherein the physiological parameter is obtained from: electrical sensing by electrodes; and oxygen sensing by a plethysmograph.
 68. The method of claim 67, further comprising measuring at least one additional physiological parameter related to temperature; movement; spatial position; sound; and blood pressure.
 69. The method of claim 68, further comprising: determining a mammal subject and region-specific optimized driving voltage provided to an optical light source; and powering an LED optical light source with the optimized driving voltage, thereby ensuring the LED optical light source intensity provides sufficient signal to an optical detector without saturating the optical detector.
 70. A non-transitory tangible computer-readable medium storing instructions which, when executed by one or more processors, cause the method of claim 64 to be performed. 